I have a serious question about mmr

Why do I always get feeders when I que with my friend who I'm trying to level (He's level 21).

Basically, when I que by myself I get even games, my mid and my top laners know what theyre doing, win or lose, they can outplay and they can be outplayed and even games are fine with me, I wish I had those when I que with my friend.

But when I que with my friend, my god, their team play like mid gold, and ours is, idk, below bronze, I can't even describe how horrifying it is, and the more this happens which is like EVERY SR game I que with him, the more frustrating it gets! shouldn't in theory the enemy team be as "bad" as our team if our mmr is poor? therefore they shouldn't be super fed in lane and should go even? And then we should be able to climb out of that mmr yes? .... apparently not, I've even seen the enemy team know how to prep baron, I can't even hope the teams I'm getting when I que with friend know how to do that, does Riot strongly disapprove of me playing with my friend or something?

My friend usually is supporting me while I adc (I'm not really good adcing but I practice for him anyways). I'm not saying im an amazing player but the difference between their team vs my team is....alarmingly huge every game, why is this?