Poorer people who would just stare do not buy tickets. Simple as that. When the price gets very high, you are filtering attendees by who has a lot of money - not by enthusiasm.

If the ticket is cheap for me, I can go even if I don't like the band too much. And with very expensive tickets, many enthusiasts won't pay while rich non-enthusiasts are bigger part of audience.

Meanwhile, if tickets are cheaper but you have to jump hoops to get them, you get enthusiasts.