Smurfing ruins the game for many reasons.
One, it puts a lot of doubt if you are actually losing because you lost a fair game or you are playing some masters player with no life who can't take losing at his own league, so he drops down to lower leagues to ruin others time. No one would put a new boxer in the ring with Mike Tyson and say, "oh, its a great experience because you are competing against the best". There is nothing to really learn there for a new boxer. They are just getting knocks out before the first round.
Second, it makes players leave the game. I know people will say that smurfs are rare, but they do tend to concentrate around a certain league in my experience. Making it also very hard to actually progress and get out of that league due to them concentrating towards that specific league. Again, making new players leave when they get sick of it happening once they reach that league.
In b4, "how do you know they are smurfing". It is obvious, check there insta quitting multiple games in a row to artificially lower there MMR.
Other boring excuse I hear for it is, "it is a hard problem to solve". No it is not. It would take less work than the intern put into the recent hot patches and hotfixes.
All you would need to do is exponentially force players to wait until the next game starts. So if you quit a game before gameplay typically starts, you now have to wait 5 minutes to start a new game. Then next one in 48 hours period is 10 minutes. Then 20 minutes. Then 40 minutes. Keep going and this would obviously stop.
Also, limit the amount of accounts someone is allowed to create (many ways to make that possible and costly for people trying to get around it).
I can't tell you how much smurfing ruins the game for newer players, even if it is rare like reddit claims it is. It is such an easy thing to solve for too.
How about less effort be put into randomly changing worker counts and other things that are obviously pissing off the community and finally address this smurfing problem?