Applause, Applause

I recently attended a play and at the end we all whooped and applauded as the actors bowed.  It got me thinking--why are we doing this? I didn't think the show was that great, but even if I did, do I need to reward the actors with my applause?  They're not doing me a favor, I paid to see this. In fact, I paid a fair amount--quite a bit more (even at half price) than I would to see a movie with a $100 million budget*.  Meanwhile, the actors are getting money to do this. I should be grateful?  It's a simple transaction--I give you money, you put on a show.  Unless something is exceptional, why make a big deal out of it?

I don't think I've ever sent my compliments to the chef, and only a few times have I sent a letter to an author (usually to send a correction).  Is it only actors who are so needy that, in addition to paying them, I've got to applaud when they're done?

*Even stranger is applause for a movie.  It happens occasionally and I always wonder who are they doing it for?