Really great songs that currently do not exist on any format including mp3

How is it possible that a recording of such a pants-shittingly great song as Valerie Carter's "Drifting and Dreaming Of You" (played over the opening montage of 70s trucksploitation classic and Jan Michael Vincent vehicle White Line Fever) does not exist? Google turns up no soundtrack to the movie. It isn't on any of Valerie Carter's albums (her early ones are all great by the way). No slsk luck at all. No luck even finding a copy of the single - surely they released a single??

And there isn't even a DVD release of this particular movie (also strange), so even if I was truly desperate to get a copy of the song, I couldn't even do the old "RCA out to the tape deck" trick.

When I first started dropping in on ILX a few years ago, I was similarly stumped by a beautiful Buffy St Marie song that was played on an episode of Sesame Street but has never been released. Still no luck tracking that one down anywhere.

How come I can find mp3s of records that existed in quantities less than 100 in 1968, and there are no less than two copies of Don Johnson's "Heartbeat" single in my fucking garage right now, but I can't find songs by two of the more popular female singers of the 1970s??