Because copyright lasts an obscenely long time so record labels can continue to rent seek and grab a large share of spending on music for work performed many decades ago.
This is not replacing artists with ai which is what is being discussed.
Spotify replaced artists with ai, they have no need to pay labels to do it.
People like to listen to the music of their youth, record labels would still be needed for many decades to come to provide a comprehensive streaming catalog.
Any service without the biggest music acts of ~1970 to 2020 isn’t going to go far.