Why are braces so expensive now?

They aren't. Orthodontic costs have actually gone down since the early part of the 20th century when they became available. Since the 70's, orthodontic care has not kept up with the cost of living index. Having any service done has a value attached to it. I would hope that having braces and treatment done correctly by a trained individual would be worth the fee you agree to pay for the service.
They are NOT. When my father practiced orthodontics, in the 1940's 50's and later, he would tell patients that treatment costs about what a new car cost. Do the math... The cost of even a modest car is 10 or more times the cost of braces.
Braces. Inflation, material costs, cost of living meaning we have to pay our staff more. In fact, everything has become more expensive and will continue to do so.