Oddly enough, pianists not knowing how to tune a piano is an anomaly in the music world, as most other artists know their instruments inside and out. The Times did a piece on this just the other day: https://www.nytimes.com/2020/11/12/arts/music/piano-tuning.h...
Most professional musicians know their instrument very well - and still know a man for the "hard" stuff, e.g. for thorough maintenance or repairs that require craftsmanship.
And there are obviously variants. The guys that fix their instruments regularly and experiment with e.g. cooking your stings, and musicians that hand them in for the tiniest, easiest tasks.
