The only somewhat justifyable reason is to be able to play with your lower elo teammates. I peaked somewhere around Plat1/Diamond before emerald was a thing, and so I needed a smurf to play with my friends in silver or below. Nowadays smurfs are probably even more necessary since Emerald adds another gap preventing people from playing with their friends. If you're playing on a smurf solo, you're actually a troglodyte.
real question, why do people smurf when theyre high elo? are there benefits
either to get a new account up in rank, or they just are having fun/getting content against worse players
The only somewhat justifyable reason is to be able to play with your lower elo teammates. I peaked somewhere around Plat1/Diamond before emerald was a thing, and so I needed a smurf to play with my friends in silver or below. Nowadays smurfs are probably even more necessary since Emerald adds another gap preventing people from playing with their friends.
If you're playing on a smurf solo, you're actually a troglodyte.