In most games at least you get to spite people because hacks get wacky
Fighting games, on the other hand, you're pretty much cheating to... not play? If you configure a macro for every single thing that takes a load off your mind then there's no purpose. The other player might get annoyed but they can simply quit, and losses are inevitable in a fighting game so it's not a big deal
I've known people who in low-level play spammed moves opponent didn't have a counter, abused glitches, ran away till timer runs out, or did other annoying stuff that's just unfun. No practical gain from that (even bragging rights since it was at home), and no real entertainment... Special mention for stealing health items while being at full health when you need them in co-op games.
They do it because they have an emotional response to deceiving someone. If you played with people like that on couch or arcade, there's a tell-tale smirk after winning that someone shows when they play just to beat you and not because they enjoy playing.
Many don't understand playing for fun. I am better than most people I know IRL at fighters, and a friend looked at me with surprise when I casually threw a round after winning one*, and when I let his little sister win, he looked at me the same befuddled way people do when you refuse to drink with them (I also don't understand why that makes them feel insulted).
*it's considered ethical and comes from casual play in arcades, nobody wants to be stuck playing CPU, you extend the play time because ultimately, your opponent isn't the enemy, so you value playing longer more than guaranteed win.
We had a few network games of Red Alert with the same dude, and it ended up with 2/2 and one of the games was a long stalemate, he later lectured me on why I didn't X or Y because I could win. I was like, why do you care so much, you won and we're even. He couldn't answer, the
idea that I don't care about losing felt alien to him. It's like kleptomania when people can't help but take others things, but here they can't not cheat or abuse something if they can win at any cost.
And I'm someone who loses on purpose to CPU in single player games just to see death animations. Some do not understand enjoying the process, they might as well skip the race and only play the podium part. For them, cheating online is sometimes a reward of its own, duping someone IS the prize.