As a kid, I just assumed it was aesthetic. Like, someone for an audience of non-musicians to project themselves on to.
As an adult, I recognize that this is almost certainly not the case. Presumably the conductor plays a role that is necessary and helpful to the rest of the orchestra… but I’ll be damned if I can’t quite figure out what that is. Surely its not just timing? Can’t the players just… listen to one another to work that out?
Random info: batons - that stick that conductors wave around - are much more common with orchestras and much less common with choirs. When you’re conducting singers you can also send signals about consonant timing, vowel shapes, and other lyrical aspects that might have more natural representations in hand shapes than baton movements.
Personal style is a huge factor in how you conduct too. Some people are up there yanking their entire body around to every beat and others find that excessive and showy.