[Aeronwen]

There's room for $15 million movies because it's a relatively cheap gamble. They can risk releasing a few cheap movies a year, hoping that one becomes popular enough they can milk the IP dry. Or they find their next big actor/actress.

But past the cheap gamble phase, studios start doubling down and throw in big name actors, and start advertising the crap out of it, hoping to get people to watch it. There's no $25 million movies, because they end up $50 million movies.