I will never understand that, I guess it all comes back to how you're raised and what kind of moral values are taught to you by your parents.
I personally never have the need to make sure the enemy team knows they're losing by either talking shit in chat, spamming the emote, spamming the dance while refusing to hit the Nexus, or any other form.
And yes, you can say I'm sensitive, maybe so. But there seems to be something about either pvp video games in general or specifically League of Legends that brings that side of the players onto the surface.
I'm fine with losing. You beat me, I say "gg wp, you were better, cya", but some just want to make sure you feel shitty after the game. I'm really going to start muting the enemy team from the start or just disable All chat in my settings.
It's just sad, that's all, and it sucks, because I know a lot of players get tilted when the enemy does that to them.