I attended one of these programs (Startup Institute Boston, back when it was Boston Startup school and free) and I had more job offers than I knew what to do with coming out of the program. The most money I was offered was $80k. I think $100k for someone just out of bootcamp is very much the exception, but I believe it does happen.
It seems like you're confusing listed job requirements with actual hiring practices. They don't have that much to do with each other. I don't think every graduate of a developer bootcamp is necessarily qualified to go right into a full engineering role, but more than enough are to make it worth it to employers.