It was Sony's proprietary format, the only one they sold, and they sold it with DRM enabled meaning the files couldn't be shared across devices. I had a Sony Walkman, bought one album off Connect, and lost it when Sony closed the store. Well, it's probably still on my Walkman who's battery is likely dead. But I can listen for free on Spotify anyways.The DRM was optional. It was inherent to the medium. The same is true of AAC.
I dunno what this line of discussion is heading towards or what spawned it. Does it relate to PS5 at all?