This is exactly it.
The system is designed to pressure you into making a decision.
Imagine the situation. You've accepted you'll pay £150 for a ticket and spend anything from 4-6 hours waiting for your chance. When you get in, your heart rate is up and you see the tickets. But they're more expensive. There's a count down timer which will boot you out if you don't buy. The rational part of your brain is saying no, but you want the hit of the purchase and you can afford it (just). So you dig out your credit card, get the hit and then the long and precipitous drop happens. A lot of people can't figure out why they did something so stupid, they just did.
Ticketmaster knows exactly what it's doing and the ways to encourage people to spend recklessly...