Heart failure is common among those who bulk up too much, with or without steroids.
The cardiovascular system can only support so much and muscle requires far more resources than fat tissue.
That said, the accumulated toll of past injuries may have played a role.
Lots of the old time bodybuilders lived normal length lives, even though they used a bit of steroids. Bodybuilding only became deadly when steroids were overused and other things, like HGH or insulin were incorporated.