Why do some people just genuinely smell terrible?

Just a genuine question because I don’t understand it and I’m frustrated. At my job and in my department there’s 3 of us that work together. Me and the leader always talk about this to. One of the guys we work with who’s a super good dude and a great worker, just smells like complete shit. Like it’s really bad. If you walk in a room with this guy you can smell it. God forbid you end up in a small office with him and you’ll damn near suffocate. I just don’t understand it. How could you possibly smell so bad almost every day consistently? Is he just not showering or that’s his natural smell? This post is also to vent but I genuinely don’t understand it. The leader has told him MANY times and he just apologizes and it continues.