Sometimes I use this tool so search all of craigslist at once, every once in a while I come across cool finds but this one was a bit odd. I'm assuming it's a fan creation, but curious if folks have ever seen this before?
I'm certain your suspicion is correct. Moreover, I wouldn't assume these were necessarily of good quality. My guess is they were downloaded from somewhere and burned onto these discs and who knows what those downloads sounded like.
Also, sometimes, a non-film score buff uses "soundtrack" broadly to refer to the entire audio component. So these may be simply the audio of complete "Star Trek" episodes (dialog, sound effects, music) simply for falling asleep to, or what somebody used on portable CD players or a car CD player on long trips back in the day, etc. Sort of a modern equivalent to the old practice of using a tape recorder to record the audio from a TV speaker.
Except the episodes we see didn't have scores written for them. They used stock and library cues. This very well can just be audio recordings of the episodes themselves.
Seems likely. Anyway, if you have the series on DVD or Blu-ray, and you have the LLL CDs, you'll never in your life actually play these recordings, whatever they are. They'll just take up space, and they will be one more pile of stuff your heirs have to dispose of when you depart this life.
This very well can just be audio recordings of the episodes themselves.
Scores I'd understand because I'm "one of us," but the only purpose I can imagine for burning the episodes' complete audio soundtracks to CD would be so a CD-tethered (like me) fan can listen to the episodes on a portable CD player, like one would an audio book.