You want an honest answer? Here it is:
It is because they can.
That's all there is to it. There is literally nothing stopping me right now from going onto For Glory, finding the easiest opponent who clearly has no idea what they're doing, and taunting/tea-bagging them endlessly or spamming or even insulting them with dozens of Tags.
The only thing that's truly stopping me from doing things like that is because I try to be good person, and also understand that there's always going to be someone new to the game and/or really young playing Online. That and my peni-I mean ego isn't so small that I need to stroke it by making others feel miserable. Others on the other hand do not remotely care for any of those factors and more. The way they see it is you suck, they rule, and they want to rub it in cause there is nothing stopping them. They can, and they find it hilarious.
It's just how people are especially with Games that can be played Online. There's no real punishment in store for them.
Report them? Good luck doing that seems how they leave the lobby immediately after all of that. Even if they do stay, they obviously don't care about getting reported. So what if they get sent to Ban Land? They still get to play with other players. Not much of a punishment.
Point is, this isn't something you can control and people like this are going to exist in just about every single Game with an Online Functionality. It's annoying and it certainly sucks; however there's really nothing we can do about those kinds of players. No matter how many we report and block people like that are still going to exist. There's really no point in stressing so much over it in all honesty.
It's okay to be annoyed and vent (cause we all need to once in a while) but remember there's not much that can be done.
Also, real quick, another honest question: Why are people such ********, even when not playing, just watching, about "Salt"? Why do you feel the need to piss people off further? Even announcers and commentators do this, and every time I hear if I find it unnaceptable poor sportsmanship. WTH?
This is something I never understood about Tournaments.
Again, people will be people. Sometimes people feel like it's deserved to rub it in someones face while others feel one shouldn't get that angry to begin with. Honestly though, agging them on only makes things a lot worse. No one wants to be publicly humiliated, and it's no wonder why some of them lash out the way they do. It's pretty sad, but it's just one of those things that exist and happen unfortunately.