> I don't see why the venues and artists don't want to capture more of what people are willing to pay

Because artists don't always want to extract the maximum money possible from their fanbase?

Artists are not always rapacious capitalists. Sure, they want to make money from the show, but a lot of them also genuinely want to reach people who may not be able to drop hundreds of bucks on a ticket. Always selling to the highest bidder is a recipe for larger acts to only be accessible to the wealthy. And as surprising as it may seem, some of them have views on that sort of thing.