I think it has to do with the amount of results one gets during those few first cycles that helps determine if the go back too.
I've known guys that had modest but decent gains, and they decided not to go back or atleast not go hardcore with it, because the amount of effort, etc.... wasn't worth it to be in a constant state of use, etc......
Then I know guys that were hyper responders that put a couple #100 pounds on their total or became new men physically in those few weeks they were on, that it would be a huge blow to their psyche to get off. The minute they went off, they were counting the days till they could get back on or jump right into the blast then cruise mindset.
Other things were age, and how ingrained they were into gym culture, etc..........