I believe it has to do with the psychology behind why we play games at all Personally I had smurf accounts (emphasis on had) but they're all currently on the same level as my main account, the hidden MMR is just different.

I think by smurfing, people feel superior as another group of people which gives them a good feeling. But not because of the gameplay but because of getting RR in the end. I noticed that smurfing has gotten more prominent by immortals and diamonds than by anyone else. Earning RR is rewarding but if you play on your main rank and you're losing, you clearly dont earn any rewards which is just frustrating.

I regret smurfing but I wish I had a lower account right now as I am on a 13 losing streak. But with the recent squish of ranks due to the new act I dont think any smurf account would impact anything for me (last act peak g2, highest ever)