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?
Timing is the most important job (I was a drummer), especially if there are tempo changes. But another important thing they do is signal for solos and control the different sections’ volumes. They are there to ensure everything goes smoothly and the audience gets the best performance possible.