Given the prevalence of heart failure, I'd say that is almost certainly the primary cause, but it's a pretty hard-living profession where excess is encouraged in almost every way, which can be quite hard on the body generally. Joint replacements are very common - Hulk Hogan had both hips and knees replaced in his 50's as an example.
I think that it's a pretty grueling vocation.
John Oliver actually did a piece on it, and that was fairly revealing[0].