It’s the labels (i.e., those who distribute the music). When they provide liner notes, the services (at least Qobuz, the one I use) makes them available. It’s really disappointing not to have them for so many releases, and it’s puzzling why small jazz labels, for example, so rarely include good information about the personnel on a release and related information.
Why don't streaming services offer album liner notes?
Couldn't they scan in the album or CD liner notes so you get all the information that would be available had you purchased the recording?
I miss them.