a lot people haven’t stored music locally for a decade or longer
Yeah, digital sales have greatly outpaced physical, but more people are discovering how little control they have over “their” music library.
The alternative to “building a library” is to stick with services that will constantly increase in price & decrease in quality. You have no control over whether your favorite band(s) are available, and no recourse if their catalog disappears for whatever reason. You will be forced to scroll through “suggested content” (ads) regardless of your subscription, and the musicians see depressingly little of the money they make for the service.
“Building a library” can be as simple as buying an album based on a song you enjoyed on the radio. There’s no “lock-in”, there’s no always-increasing monthly bill, and there’s no chance of the store saying “uh you can’t listen to that anymore”. It’s dead simple, but certainly not as flexible as streaming.
Side note - I’m absolutely the type of person who would take the time and “re-build” my library, but I acknowledge I’m in a small minority of people, there. I also love shuffling through playlists which is impossible to do with physical media. Until I find a magic answer I’m right here with the rest of you with a streaming service.