It is a team game, but the fact that it is played over the internet instead of in person allows people to more easily dehumanize others, and allows players who are unsportsmanlike to more safely get away with their shit talk.
In League, your team mate dies three times in a row in top, all you see is them dying. In Baseball, your pitcher gives up three home runs in a row, you can see him getting pissed off and frustrated more than anyone else on the team is, and therefore you know he is trying, and its just not working.
In League, you call someone trash or tell them to kill themselves, all that person can do to retaliate is block you, mute you, ignore you, report you, or flame you back. In Hockey if you call someone trash or tell them to kill themselves, you might just get punched in the face.
The lack of proximity makes it harder to empathize with another player, and easier to treat them poorly knowing that you are safe from potential confrontations.
Basically, its the same problem that ANY online team game would have.