Every popular online multiplayer at the moment, is designed to generate money yes?
Overwatch, Dota, any popular game right now, is made so you want to keep playing. The corporate minds behind the money mechanics for this game have come about with the 50/50.
Look on any forum for each game, players always mention a pattern. People talk about the MMR, but how can that explain the team members you are suddenly put with?
Think about it properly for a second. You are with decent team members for so many games in a row, and then all of a sudden afk's and trolls appear again, for a a few games straight? That's statistically impossible. It completely goes against the law of probability.
Some exceptional players can push past the games they are given meant to slow down their ascent, but the system is designed for the main bulk of players.
The system ABSOLUTELY forces wins, as well as loses. Keep a note of your own games (including when people went afk and when people started flaming etc), you will notice the games you win there's a lot less of that.
Look to cut to the chase here, it would in no way be good for this game, if the match maker truly put you with players of the same skill. You'd never have a massive win streak, you'd just peak. You would get bored, you wouldn't buy champs, skins, rune, pages etc. You'd go and play something else.
They know FULL well that when this game starts a losing streak, players will not stop playing until they get back to the point they were before in the league, that can easily be 10 plus matches it knows most players will play. Some rage quit for a few months, but they count on the addicts. The players watching the pro events, and players looking for when new champs drop.
The 50/50 is the moba/e sports business model, designed for fanatics aged between 14 to 25, that's their core target range. They hope players in that bracket won't notice the artificial ceiling and floor it gives you. They hope you all just keep playing, and keep paying.
People who play with their friends have a chance to do better in ranked etc, they try to encourage that, but they know for a fact there's a lot of people who play solo. So that's why the 50/50 is there.
Casino's have the same practice. They give you the illusion of winning, but by the time you are ready to leave, you've more than likely put all your winnings back into the casino and walk out with a loss.