"I do not have that mentality myself"
Confirmation bias. I'm not talking about individuals, I'm talking about general demographic. If not for KO specific missions there wouldn't be any rational reason to be angry of your opponent quitting, so we're left with irrational ones, which often may be linked to persons immaturity at particular section. That's what I expressed in both my posts prior to this. I didn't modify anything.
In any case, rewards for particular KO missions usually aren't great, like at all, so it's not nearly enough of a justification to waste your opponents time. Having in mind construction of UR there maybe should be some penalty for opponent leaving on first or second round, apart from loss, depending on game mode, to prevent abuse, however it should be much lower than it is now. Third and fourth round should be a fair gain for any mode, there shouldn't be any penalty for quitting, losing is bad enough by itself.