So... plumbers require education, too. In the US it's apprenticeship, trade school, or community college to get licensed. In the UK it's similar, so not just a US thing. You do one of these routes to prove you can do the skilled labor, and receive a license for doing so.

There is not a "trade school" for a librarian, because to prove you can be a librarian, you need to prove you can learn consistently and over a long period of time. That's not possible without longer education.

Your argument makes it sound like plumbers don't require education (not your intent, I know), but denigrating the librarian trade doesn't help, either.