Song on CDs are 16bit uncompressed files. Songs on streaming services are compressed. Spotify premium files are AAC 256kbps - that’s the best they can offer. That is a huge jump.

Another factor you won’t hear people talk about is normalisation. Because streaming services are so playlist-focussed, they want the volume of the songs to be the same (so one song doesn’t sound super loud compared with the others). They do this by analysing each song and turning it up/down depending on how perceptibly loudly it was mixed.

The result? Your CD will likely sound louder and clearer than Spotify. You are right