Why are Platinums allowed to duo with Golds?

I've voiced my opinion on this before, but for some reason it always receives backlash.

I get games every so often where there will be a Plat 2/3 Gold 3/4 duo on my team. I'm not talking about a gold 3 smurf with a 70% win rate. I'm talking like, 500 games, hardstuck kind of gold 3.

There is a big difference between a player who is at Platinum 2 MMR, and a player at mid gold MMR. You can literally tell without even opgging before hand who the gold is.

They don't dodge abilities as well

There macro isn't as great

They extend fights longer than they know they should

They don't know there damage foresight as good.

It just hurts competitive integrity to get a person like that on your team, when everyone else is plat. You can look at the game I just played a few minutes ago, I can't link it here or else this post will get removed from the boards.

Make a restriction, Platinums should not be able to duo with Golds, just like Diamonds aren't allowed to duo with people under a certain level.

And don't tell me there's no difference between a plat 3 player and a gold 3 player. If there's no difference, the gold 3 player shouldn't be hardstuck with 500 games in that MMR.