Unfortunately, Primecoin creator Sunny King decided to abandon ship by focusing on other projects. After Peercoin, Sunny King made a new PoS coin called "V Systems".
Thanks for mentioning V Systems, I had searched for that one lol. Yeah, he may simply have to tried to jump on the train of premined PoS coins at that time, seeing how much money was made with them. I see their
website is still live, but indeed it doesn't really look interesting. It's still
developed though.
On the other hand, Primecoin could have easily been upgraded by Primecoin whales, just like the Peercoin folks did when Sunny King slowed down his contributions. For some time, XPM was in the top 30 on Coinmarketcap, so some people probably made a lot of money with it. Indeed there seems to have been
some minor deveopment, at least until 2022 or so.
All three,
Primecoin,
Gapcoin and
Riecoin have also still websites. But
Gapcoin's development was abandoned in 2021 it seems. Riecoin, in contrast
seems to be alive and developed actively (last commit to Github was 3 weeks ago).
So many dead coins that everyone has long since forgotten. It is much easier to list those coins that are still alive. Many people created new coins without any practical use. And soon such coins has become scams.