Normally the market is supposed to correct these things but sadly we've created a culture that looks down on physical labour. Now there is a small group that can charge whatever they want.

Is the market not supposed to reflect culture?

This is an outdated ideology. Now the market is meant to define correctness. Deviation from the perfect wisdom of the market is the only form of sin.

They can't charge that much or people will do their own plumbing. It's fussy, but most routine things aren't too hard to do one step at a time. Sometimes you get a new faucet with an internal leak though, experience might have helped diagnose that without taking everything apart 20 times. Sometimes there's a big job like replacing a lateral, which is yeah, time to hire a pro.

In the UK gas work is regulated so only a registered plumber can do it.

You're not supposed to exceed the speed limit either...

I should say I spent 10 years in the building trade and I saw all kinds of things, but I never saw an unregistered plumber fiddle with gas.

Unlike the speed limit, this rule is pretty well respected.