Why do people who play with friends get benefits?

They get party IP boosts from time to time, more mastery points, the dynamic queue system favors them, etc.

Why do you get benefits just for playing with friends? Why should just because you play with friends get benefits that us Solo Players don't? I personally its a bit bullshit if you ask me, that just because your in a group vs being solo, that you get benefits.

Essentially Riot shitting us Solo Players.