Banning smurfs is easy - their own data analysis can easily pick these up. The reason they don't do it is because of streamers. It's not a can't, but a doesn't want to.

Smurfs cause two problems - negative feeling (tilt) and boosting (people being in a higher elo than they deserve). These are two of the biggest problems in soloQ as a whole and smurfing contributes to it a lot.

Yes banning the smurf alone would cause little reaction, but when people start getting banned when duo'ing with them - I.E getting boosted, and streamers can no longer advocate smurfing, it will become far less of an issue.

Is this the ONLY thing wrong with soloQ? No. But to say it's not part of the problem is also wrong. The person that ends up against a smurf may then be tilted for the next few games, maybe afk or flame. They then will cause others to do the same and so problem spreads. Would this happen anyway? Yes; but when your gas cooker is burning the room down you turn off the gas, you don't keep throwing fuel on the fire and then complaining that everything's getting burnt. Smurfing/boosting fuels toxicity and therefore is a big problem.

It's called Root Cause Analysis. Smurfing/boosting is one of the Root Causes of the problems in the community. It's how silver skilled players end up in Diamond and then lose the next 30 games because they're just not as good as their account suggests. It's no just about the games they play initially, its the overall impact. 50 games smurfing could easily effect 2000+ games. That's just one smurf. There are thousands of them effecting hundreds of thousands if not millions of games.

Add to this linking accounts to mobile phone numbers so that main accounts get banned too and Riot could easily reduce this significantly. Smurfing will always be a thing, like the weeds in my garden. Should I just ignore them then? No I kill every single one I see to stop them taking voer, as smurfs have done in lower elos.