I find this topic, to some extent, relatable as well.
My current music library is roughly 14k songs, but It peaked at 22k at some point.
Being such a completionist (to some extent I still am), I wanted to have every soundtrack, character song collection, etc. for whatever anime series/movie that I watched.
Then during my senior year of HS a good friend of mine w/ similar interests jokingly challenged me to play the tracks on my Ipod on shuffle, some stupid soundtrack track came out and I had ZERO idea where it was from.
We chuckled a bit before switching tracks, but in my head I came to the realization that I wasn't even familiar with half the tracks I even possessed. About a year or so later (out of laziness), I went ahead and purged 7,000 songs and that was that.
Now that CD collecting is front-and-center as one of my hobbies, I've started chomping down at some of the "illegal" bits of my library.
Also using Apple Music JP on the regular, it's very possible at this point for me to go entirely legal.
Yet, my greatest fear is ~10 years from now if I become disinterested/dispassionate about the music I'm currently interested in...
While I'm confident that I'm not fickle my music tastes, I have no clue what the future has in store.