We all assume a lot. We assume that all streaming services receive the same source file. That might not be the case. We also forget that until that "music" passes the DAC, it is in fact not music, but a digital file. Any software before the DAC can, and will affect the sound. Like Spotify for instance, has a bass boost over all other services, like a "loudness" that you can't turn off. In the car it's fine, but on my home stereo, it's too much.
We also assume that all streaming services, use the same software/storage/server/OS etc. They are all different ways to deliver the bits to your DAC. Think all things contribute to slightly different sonic profiles.

