Hi @Rovon, welcome to the forum! 
I don’t know that there’s a single reason for that. Inevitably some projects don’t work, while others just run out of momentum, but some finished projects may be commercial (which sometimes means they can’t be shared in too much detail), and others may have just not had many responses, so the creator didn’t post many follow-ups.
If you’re interested in a particular project you can always post a comment on that topic and ask for any extra details you’re after - the worst response you can get is silence, so there’s not a heap to lose by asking, and you might end up with all the info you wanted
Is there a particular type you’re interested in? From a search of ‘drop camera’ there are heaps of posts, covering various different approaches. The following seem relevant, but there are no doubt others of interest too:
- Dropcam in Mineshaft (commercial, view through dome, cam in tube)
- Tethered Underwater Camera (discussion of details of a couple of approaches)
- Building the world’s first consumer deep-sea dropcam
- Building the world’s second consumer deep sea drop cam
- DropCamera System (quite extensive, lots of details)
- Towed Camera Sled (poster also has multiple interesting dive videos - you can click their username and check their ‘top topics’)
- Drop Camera/Tow Sled Frame (BlueROV2 modified for towing)
- Drop Camera Build (GoPro looking through side of a clear tube)