Why does Riot enforce split-pushing?

Riot always complains about how games are too long blah blah, but split-pushing does the exact thing that they hate. It's the most frustrating playstyle and goes against everything that a "team" game stands for. It's always the same thing,

-Player picks X champion and goes top -Farms and stays top all game(even if we starve them) -Eventually farms enough to get items and now every time that person is top, the other team has to sacrifice 2 people to deal with him because he is extremely hard to kill 1v1 -Sometimes barely escapes because that champ has some mobility -Rinse and repeat

This is the same pattern for every split pusher. It promotes little to no interaction with allies or enemies and draw out games.