I also wonder, in addition to the changes in media format and availability of streaming replacements, if the emergence of DJ controllers and being able to mix from your digital collection may have had something to do with it, too. A lot of the mix CDs I made in the early 2000s were vinyl DJ sets I recorded. Sometimes these were demos, sometimes these were special mixes I made for someone. And there are definitely still a lot of kids getting into DJing.
I'd make her a mix CD, but there isn't much music we've listened to together.
In fact, when I talk to anyone about music, the result is often a mutual "Hm, never heard of them" followed by non-interest.
Music discovery is done independently and I don't usually want to get into other people's bands. I guess it used to be more social. I'm a late millennial, almost Gen Z. For me music is personal and not social. I listen to a lot of video game soundtracks.
I have one friend whom I introduced to a lot of music and we used to share often (links to songs etc). Over time, that friend began having their own vast personal world of music and we rarely share anymore.
One of my favorite things to do with music is to create a curated playlist and imagine sharing it. Sometimes I actually will share it with that friend or my partner, and that's been well received at times, as a rule it usually feels like asking anyone else to listen to something I like is just burdening/boring them.
Possibly worse, when you actually do connect with someone new about shared music taste... suddenly you open the floodgates and actually there's way too much music out there in your individual spheres so that sharing becomes exhausting.