" And is it cognitively normal -- not to mention socially normal -- to listen to so many songs[...]on repeat, day after day after day?"
Even provided it wasn't normal, how any person engages with art is up to them and it doesn't require someone else's approval. No need for your tastes to be normal.
And as Nabokov used to point out, a good reader, that is an active and creative reader is a rereader. Same goes for music. Many incredibly talented people spend their entire lives studying and playing a handful or maybe only even one composer, so why shouldn't listeners do the same.
Interesting that you bring that up (rereading). I found that the first and foremost reason to learn at least a few poems by heart is that you will be able to "reread" them at will without the printed text: on the bus, in the shower, etc. It helps you appreciate the text so much more.
Active listening is a real pleasure. Qualitatively, it’s a very different experience to having music on in the background while doing some other activity, and it merits listening on repeat.
Mentally separating out the different voices in the composition, listening for how they enter and exit the soundstage, how that layering of sound builds up the texture of the music, not to mention melody, harmony, dynamics, pacing, phrasing, repetition, structure, timbre, rhythm, and the interplay of all these factors.
Even provided it wasn't normal, how any person engages with art is up to them and it doesn't require someone else's approval. No need for your tastes to be normal.
And as Nabokov used to point out, a good reader, that is an active and creative reader is a rereader. Same goes for music. Many incredibly talented people spend their entire lives studying and playing a handful or maybe only even one composer, so why shouldn't listeners do the same.