I don't think you understand what resetting MMR means... that would be a terrible idea.
Resetting MMR will not suddenly make you better at the game, you'll still be as skilled as you are now. MMR is calculated by comparing your hero specific stats to other people playing the same hero at your SR. So when you play rein in gold you're being compared to every other gold rein player. They further break it down by map as well to get an apples to apples comparison. If you're preforming better your MMR goes up, if you're average it stays the same, and if you're worse it goes down. The system is built on having a large group of people to compare so it can know how good GM is and how bad bronze should be. Resetting all that information hurts everyone and eliminates the baseline.
If you think smurfing is bad now, literally every single GM player will now be randomly matching with bronze, silver, gold, ect players for months. It's not even just about the best players being pushed up fast, enough good players have to play enough games for there to be a GM, which could takes months. Until that happens really good players will unintentionally be smurfing and wrecking games.
An accidental MMR reset happened at the start of season 18 and it was awful. Legit bronze players win streaked into GM and some GM streamers ended up in gold because there was no data. The system is only accurate with data and gets better the more players it has information on. You would end up getting the occasional GM player in your game destroying everyone, but there are WAY more bronze and silver players who would end up in your game and severely hinder your team.
MMR resets are horrible.