Most of our reasons have been covered by posts above. We've been members for 25 years and average 4-5 trips each year. We've been to virtually every restaurant on property, some dozens of times.
The kitchen gives us flexibility!
1. We're not park commandos any longer, so leaving the parks during the day is a good thing for us.
2. Restaurants at Disney, even though they do update their menus, get repetitive and boring.
3. Cooking together is a FUN activity for us.
4. Cooking your own food is (99% of the time) a healthier option than eating out.
5. There is a significant savings involved by not eating out all the time - just price out a breakfast out as compared to what you can do in your room.
6. We have dishes that we like that aren't too complicated - and we are not at the mercy of a specific menu if we're not in the mood for something.
There are other reasons, but these are the highlights. Nowadays, we rarely feel the "need" to eat out unless something new opens or is refurbished. We loved Topolino's when it first opened, and now? Eh... We've enjoyed some of the newer places like Woody's Roundup BBQ in Hollywood, but that's not the type of place I'd hit several times a year. We don't have high expectations for the upcoming Cake Bake Shop, but we will definitely try it as soon as we are able.
DVC has been wonderful for our family. The kitchen and laundry are HUGE plusses, especially on longer trips. I don't care if people cook in or eat out; it's none of my business. I'm not sure why this topic comes up every few years.