I wonder if they do it to be awarded as the best bber on stage or they truly want to be as big as possible leaving aesthetics behind.
At the time they made those choices, it was the early 2000s. Back then distended guts weren't being penalized and "bigger" was always "better." In a way, everyone was trying to keep up with Ronnie and Jay, so there was pressure to put on as much mass as humanly possible, and those two drugs become the vogue way of doing it. Plus, since guys from the '90s and 80s hadn't used them or hardly at all, there was no way to tell whether side effects would really materialize or not, and these guys are reckless to begin with, so they probably say fuck it, let's do it.
But in Branch's case, there's the added wrinkle of his small-man complex. It's why he won't retire until he has a near-fatal event or completely tears off a quad, something like that. Guy has been "big" since 1992. Hard to leave that behind.