People have different body types. Kelvin is an extreme endomorph, he's just naturally an extremely thick dude. You're just basing it off of his height and assuming that just because he's 5'9" and other 5'9" guys can make 155, he could too, which makes zero sense. In reality he could never, ever make 155 without cutting off a leg. He can make 170 with a very strict diet and a tough cut, but some guys just don't feel as good when they're cutting weight. People make the same argument with guys like DC, Fedor, etc. Some dudes are just thicker and it's not realistic to assume they could somehow change their body type and move down weight classes without severely impacting their performance.
