All that has changed is the environment and lifestyle humans live in, and it's quite obvious discipline and willpower cannot overpower that environment on average.

The change was far too rapid for anything else to be remotely the primary cause.

If you put a past heroin addict locked in a room with unlimited heroin readily available, chances are likely 9 times out of 10 that person is going to partake eventually. Same goes for our food environment and way of life.