Well, I have a few theories.
One is that there was a reaction to some immunity that we were injected with as a child. You know all those shots that we are required to take for diseases that are no longer even around? Well, I think that those shots, while at such a young developing age, caused a break up or some kind of cell rejection in our bodies.
If you think about it, the pancreas isn't even an organ- just a group of cells. Which means there really isn't anything protecting it like a thick "skin" or anything. So, if there's something going to go wrong inside the body- the pancreas is a very viable option to quit. This theory has begun to be backed up in scientific tests in Japan.
Theory Two is that we're a very "fat" country/ world. People seem to be getting bigger and bigger- and it's not necessarily because of how much they eat, but more WHAT they eat. T1 could be evolution trying to get us to focus on what we're putting in our mouths, and to realize the consequences of un-healthy eating. Being forced to take a shot every time we eat definitely keeps our minds on WHAT we are eating.
Theory Three is it's an environmental issue. We have a lot of smog and other surrounding ailments that we are subjected to in the air around us. Like mentioned earlier- our pancreas is a very "naked" "organ" and is subject to the bad substances that get washed through our systems. Causing it to choke up and fail.
I am the first diabetic in my entire family- I believe this makes me more focused on my body and how it works. haha.