It's a combo of a lot of things... these dudes have a ton of mass, so their heart have to work hard... add roids, add in those 'preworkouts' with a ton of caffeine and generally unhealthy portions of food to gain mass and then you get what we see. Kali got off the roids and lost a lot of weight but he probably seen his views slipping and got back on... but he has to consider his health first.
It's kind of crazy, but we're literally entertaining ourselves watching guys kill themselves slowly... sort of like watching that badland chugs dude