1. They Grew Up Doing It
For many people who grew up in Jewishly observant (and that doesn't just mean Orthodox...) homes, keeping kosher is part of the fabric of their lives. It's what feels normal, and whether they do it out of habit or personal religious conviction, it's hard to imagine doing anything else.
2. So Kosher Observant Friends and Relatives Can Eat In Their Homes
There's no denying that gathering around the table to share a meal with friends and loved ones is one of life's great pleasures. If family members or close friends keep kosher, the desire to host meals can be big incentive to keep a kosher home.
Parents with children who become more religiously observant, for instance, may decide to keep a strictly kosher kitchen so that the whole family can dine together -- even if there are varying levels of personal observance within the family.
3. They're Lactose Intolerant or Allergic to Dairy
Not everyone who seeks out kosher food does so for religious reasons. But since the laws of kashrut enforce a strict separation between dairy and meat, people with dairy allergies or intolerances can rest assured that if a kosher product is certified as meat or pareve, it is free of all dairy.
4. They Believe Kosher Food is Cleaner (or Healthier or Safer)
In order to obtain and maintain kosher certification, food production facilities are subject to potentially frequent visits from kashrut agency representatives, who help ensure that the factory is meeting kosher standards. Some manufacturers, caterers, or restaurants will even have a mashgiach (supervisor) on staff for constant on-site kashrut oversight.
Many assume this extra layer of production supervision means the food is "cleaner" or held to a higher food safety standard. In the case of insect adulteration, that may be true -- kashrut has very little tolerance for the consumption of nearly all insects, so there's a lot of attention paid to ensuring that produce and grains are bug-free.
But though kosher means "fit" to eat, from a technical standpoint, halacha (Jewish law) is not particularly concerned with whether a food is health-promoting or made in a pristine kitchen. There are plenty of kosher products that are full of additives, trans fats, or an abundance of salt or sugar. And kosher supervision is no guarantee that a restaurant or caterer has a HACCP plan in place, or employs safe food handling techniques.
5. They're Concerned About Animal Welfare
Along similar lines, many Jews and non-Jews alike who are concerned about animal welfare feel more comfortable purchasing kosher meat, because the Torah takes a strong stance against causing tza'ar ba'alei chayim (the suffering of living creatures). Shechita -- ritual slaughter -- is intended to be as humane and quick as possible, in stark contrast to the realities of factory farming and industrial slaughterhouses.
Nevertheless, in recent years there has been a backlash against ritual slaughter in certain political arenas, with some nations outright banning it. While the campaigns to ban ritual slaughter tend to rally behind animal welfare concerns, many question if they are in fact motivated by Islamophobic and anti-Semetic sentiments.
The truth is, if one is going to consume meat at all, it's necessary to accept that an animal must be slaughtered to produce that meat and that the process is bound to inflict some stress or pain upon the animal. Theoretically, proper shechita minimizes that pain, as the animal must be slaughtered swiftly with an incredibly sharp, nick-free blade. This is not to say that the kosher meat industry has been free of controversy related to factory farming methods and questionable slaughterhouse practices. But there's been a recent renaissance in terms of embracing ethical animal husbandry and shechita, as evidenced by the growth of outfits like Grow and Behold and Kol Foods, two purveyors of sustainable, humanely produced glatt kosher pastured meats.
6. They're Vegetarian
Jewish law categorizes foods as meat, dairy, or pareve (neutral). Meat and dairy must never mix, while pareve foods, such as produce, grains, or eggs can be consumed with either meat or dairy foods. (As a side note, fish is considered pareve, though Orthodox Jews typically refrain from cooking fish and meat together, or consuming them from the same plate).
In any case, these categorizations simplify food shopping for many vegetarians. If a product is certified kosher pareve, it is necessarily free of meat and dairy, and so suitable for vegetarians. Similarly, lacto-ovo vegetarians can purchase kosher dairy foods without worry that they might contain meat products.
Incidentally, though kashrut purists maintain that Jews who keep a totally kosher home yet eat in non-kosher restaurants don't really keep kosher, a great many choose to do just that. By consuming only vegetarian food (and sometimes kosher species of fish) when dining in non-kosher establishments, they adhere to the spirit -- if not the letter -- of the laws of kashrut.
7. They're Halal-Observant
Though not identical, there are many similarities between the laws of kashrut and halal. Both observant Jews and Muslims refrain from eating pork, blood, and dead animals (e.g. those that died of natural causes, illness, or attack), and proper ritual slaughter is necessary to render an animal fit for consumption.
In recent years, there's been growth in halal certification, but particularly in the U.S., it's still far more common to see food products with kosher certification. While not all kosher products are suitable for observant Muslims -- products containing wine or alcohol, for example, would be off-limits -- many seek out kosher meat or other kosher products if halal-certified foods are not available.
8. To Preserve Tradition and/or Embrace Jewish Identity
French gastronome Brillat-Savarin famously asserted "Tell me what you eat, and I will tell you what you are." Without a doubt, keeping kosher is a lifestyle and one that defines the eater and provides clues about the community to which she or he belongs in many ways.
Of course, there are also many traditional foods that resonate as specifically "Jewish," and their preparation and consumption is vital to the creation and preservation of family traditions, holiday celebrations, and day-to-day life.
9. To Promote Mindfulness About Food
Keeping kosher isn't just about the foods one may or may not eat. There are also many rules about preparation and consumption. There are waiting periods of varying length between meat and dairy food consumption. There are blessings to be said both before and after dining.
In other words, keeping kosher is a detail-oriented endeavor and one that requires discipline. But the structure can promote mindfulness and heightened awareness about what, how, and where one eats. And for many, that mindfulness can promote appreciation, joy, and deeper spiritual insight.
10. Because G-d (and/or the Torah) Said So
Though it sounds a little flip, this is actually one of the simplest, most straightforward reasons that observant Jews keep kosher. For all of the philosophical, ideological, even quasi-scientific reasons people put forth to help explain kashrut, at heart the mitzvah (commandment) to keep kosher is considered a chok -- a law that cannot be explained by logic alone.
That's not to say that keeping kosher is a matter of blind faith, but rather that embracing kashrut signifies an affirmation of G-d's wisdom and a willingness to accept the Torah's laws.