I must reply to the original poster, as many of you have, that it is dangerous to make assumptions about why so many people get T2. First of all, for some people who are overweight, it is as much due to an addiction (and yes, a real ADDICITION) to eating as it is for a drug user or alcoholic. For others, being on certain medications can cause weight gain. And yet for others, they may be diagnosed with T2 despite being thin. I, myself, am one example. I was quite thin when initially diagnosed and while I might not have been tested then for antibodies, I was tested at a later date and showed no antibodies. But T2 runs in my family on my mother's side, so there's definitely a genetic component.
Same holds true for my best friend, who is not only thin, but actually underweight, and who is a fitness nut. She works out four days a week at the gym, one day with a personal trainer, and goes for a walk on the days she doesn't go to the gym. She also has a family history of T2, and is currently pre-diabetic.
Also...what about all the overweight people (and cats) who are NOT diabetic? How does anyone explain why some people and animals who are moderately overweight develop T2, yet many people who are moderately overweight and even some who are morbidly obese, do not develop it? No one really knows for sure. All we do know is that for some people who develop T2 and who are overweight, losing weight will help them stay off medications, yet for others in the same condition, they end up needing insulin.
As others have said...a very complex problem.