I just don’t get it

First let me get a couple things out of the way. 1) I'm a really mellow gamer, and person in general. It takes a lot to piss me off, I may get down and kinda sour every now and then, but never really pissed, that takes a rare breed. 2) I love the local group I play with. Almost without exception they are casual gamers that like to have a good time and they are awesome friends, my adopted brothers and sisters.
Now that's out of the way, you'll notice up there I said almost. There are a few players that make my blood just boil quicker than water on the sun. And in all 3 cases it's come down to one action. Cheating. I don't get it. Not even a little bit. What makes a person reach over and decide to do something they KNOW is outside the rules? I don't play that way, the majority of the people I've ever played in any format at any store don't play that way. So what, if anything makes these people so, I don't even know what word to use, overcompettitive maybe, that they have to break the rules to win. To me cheating is the ultimate way of saying you disrespect the person you're playing against and in some small way, disrespecting the system you're playing as well (although I'm sure we've all wanted to disrespect Games Workshop in some fashion at some point, just don't do it on the table). Maybe it's just my nature that keeps me from going "ohhhh I get it, that's why they do it" I'm not a real compettive guy. I like to win, everyone does, it's the being ok with losing that I think these people have trouble with. But even if I wanted to win so badly I couldn't stand it, I couldn't reach over and try to get that extra quarter inch out of that movement, or move my tape so that it's off my base when measuring for a charge, or not taking dangerous terrain checks hoping my opponent isn't paying attention. To me that cheapens the win, it's not worth it anymore, it'll always stay in the back of my head that I did something wrong to get that win. I suppose I should feel honored that I'm so good that they felt compelled to cheat against me that it was their last ditch response to win, but I know that's not true. Most of the people I see cheating do it against everyone, if they're winning or not. It's just something defective in them that makes them think it's ok. Now, I want to be clear here, I'm talking about straight up breaking of the rules cheating, not little things that, while disrespectful, don't harm the game. Stuff like rolling your dice behind terrain so your opponent can't see them. I can't call that straight up cheating, but it does make it look like you've got something to hide. I can tell this rant is starting to lose focus so I'll just end with this. Don't be a dick. Have enough respect for yourself and your fellow players to not do that shit. After all it's just a game and if you lose sight of that, maybe you should stop playing.