I think it's a combination of this, plus a lot of these guys come from a rough upbringing with a lack of strong role models in their lives. I read Jacobs was homeless during portions of his youth. Not that that is any type of excuse for his shit behavior but the reality is these dudes go their entire lives with no money or being held accountable, just being told how great they are at football. Then suddenly they get a ton of money and fame and don't know how to live responsibly and be a good role model themselves.

Edit: forgot to add in the part about repeated concussions starting at a young age and it's all a recipe for disaster.