Why would actors/celebrities join politics?

They would have accumulated wealth from their acting already.

More often these actors never succeed anywhere. They spend crores of rupees in political campaigns and then they join forces with some other parties. How do they financialy gain from this? I'm trying to understand what logical reason would they have to enter politics?

If you are a celebrity with 100 crores in assets you'd just want to retire and enjoy the life. Atleast that's what I'll do.