Oooh! I was just talking about this with my wife, who I met gaming online. We've had the conversation with each other, and other people a lot, including cheaters.
So, most of the cheaters I've known tend to look at it as entertainment rather than competing. It isn't that they want to beat other people, and think cheats are an acceptable way to do that. It's usually that, regardless of their skill, they get bored with the slower pace of play, but still want to play.
I'm not saying it makes sense, or is acceptable, but that's the most common explanation I've heard.
The next most common is the jerks. They do it either to mess with people, or to "troll" people that the cheaters think are too serious, or too invested or too "tryhard", or whatever the excuse is. That kind of cheater does indeed wnat to ruin things for other people.
The next one that I've run into enough is the nerds that are just looking for ways to cheat as a hobby. They're the ones that end up developing cheat tools, whether or not they let others use them. It's about figuring out the game, its code, and how to manipulate it. Those players tend to stop using cheats once they've done what they wanted.
The other significant grouping I've run into are the ones that only cheat on PTW games, where they'll say that if you can pay your way to winning, the game is already a cheat. I actually agree with them, but I just refuse to play those games, even if they're otherwise very good. In theory, I would maybe cheat in those games if I knew for a fact everyone playing was cheating too.
I've actually done that once, but on a private server where nobody could play without an invite. It was actually kinda fun running an over powered character by virtue of a ton of free "pots" that would buff you in both pvp and pve play. Everyone was juiced up and one-hitting each other. Wouldn't be fun all the time, but the free pots were only on weekends, and outright unavailable any other time.
And, I will sometimes run cheats in single player games for the same reason; it gives a different play experience that's fun as long as you can turn it on and off.
But you'd be surprised how many people in all of those groupings will cheat if they think there's other cheaters, no matter if there's proof or not.