Jon Ritman (I know he later did a Game Boy game), Clive Townsend... And even the 2 guys who did the early action Lucasarts games.
What happened back then? It's quite surprising so many of these star game developers only worked on 3-4 games according to Mobygames.
Difficult, highly skilled work, long hours and low pay, I would guess are all contributing factors. People start families and don't want to sleep under their desk at work any more. People get fed up and take their skills into other industries. Richard Aplin is another one I believe? As was Dennis Caswell (creator of Impossible Mission).
I noticed recently that Peter Liepa, the guy who gave us Boulder Dash, has no other game credits either. You have to really love games to want to stick it out in this industry. Smart, highly skilled people can make more money, more reliably, with better work/life balance doing other things.
I would guess that having the programming skills, most turned to using their skills professionally to business, I.e. supporting banks IT infrastructure etc.
Jon Ritman didn´t left the industry before the 90´s. He worked on two unreleased projects before doing Monster Max and Super Match Soccer: Final Whistle (Arcade) and Soccerama (Snes). The same happend to many people.
There´s also a huge lack of credits in Mobygames. Don´t rely exclusively on it.
I can't speak specifically for the "star 8-bit developers" but I know that many people in the gaming industry struggled to transition to 3D programming around 1994 (PSX, Saturn, etc).
On a positive note, sometimes these "star" 2D game developers leave the industry after only a few years... to become stars of other industries (or at least fund revolutionary companies).
For example, Stephen Grand, who created the revolutionary Robin Hood and Rome games in the early 90s, and then released the unique Creatures series, changed games around the year 2000 for... robotics and AI! And he even received an Order of the British Empire.
I recommend reading the story of Steve and Creatures. With Creatures in particular, there was a known troll who was torturing the creatures, which was bad, but was good for experimental reasons, and he received lots of online hate 20 years ago from game fans.
SOURCES:
https://www.mobygames.com/person/23531/stephen-grand/
https://en.wikipedia.org/wiki/Steve_Grand_(roboticist)
https://www.howwegettonext.com/the-brain-in-the-machine/
https://reddit.com/r/HobbyDrama/comments/mxcq2i/video_game_creatures_or_how_the_us_navy/