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.
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 New Zealand, water work is regulated so only a licensed plumber can do it. The prime minister was once investigated by the Plumbers, Gasfitters and Drainlayers Board for installing her own toilet. Her punishment was having to apologize :P
