Why MMR deciding what team you should be on doesn't work.

Ok, So I'm far from a good player, however, i like to believe I'm Halfway decent So why is it if you are doing well and get onto a winning streak. Does league put you with people with lower MMR than you, often people who are new to the game or they haven't learned much about the game and will just get destroyed in game?

I believe the point in this is to attempt to provide the best win chance for each team. However, that means if you're doing well in games you will go against harder and harder team which makes perfect sense, however, at a point it becomes, You go against good teams while bad players because your MMR is being used to even out the others.

I'm not trying to make a post ranting about bad teams or anything like that. I just wanna know why cant Match make up be random rather than based on MMR trying to even out amoung both teams, yea So you might get a point when your MMR is a lot lower than the team, However it has a chance of stopping Every lane from losing and only 1 possible. Anyways curious what you guys think.