For my wife, it was partly a social thing- her friends did it, and she is in sales and this actually became a popular thing to take clients to. She had expensed over $10K in classes her peak year. She became friends with some of the people that worked at her favored studio, and even some of the instructors (which appears to have been not unique to my wife but cultivated by corporate culture: https://www.vox.com/the-goods/22195549/soulcycle-decline-reo... It was a Thing, and in NYC once something is a Thing, it becomes unstoppable and takes on a life of its own.
Its not even a full hour, the standard class is 45 minutes IIRC.
But paying $35+ for a single one hour spinning class?
Pricing like this happens when there are enough people that can afford it without thinking about it, and they don't want to be surrounded by people who can not afford it.
It's a smaller scale version of a town with very high taxes, and no extra benefits for those taxes.
Its not even a full hour, the standard class is 45 minutes IIRC.