I can speak for stuff I've been involved in and why they've either stopped or have been put on hold.
I was working with Fragmare on Xymati but it was requiring a level of competence above and beyond what I was capable of at the time. I just didn't have the skills to program all the stuff it required. That's not an issue nowadays, now it's just time. Maybe it's something that can be picked up again in the future.
Monolith basically ran out of steam, so to speak. I was having more and more issues in my "real life" and was neglecting the project, so people split, thinking it was a dead project. However, it has a complete soundtrack custom-made for it by a professional musician, and it's part of a quadrilogy so it will eventually go back into production. The game engine was an important evolutionary step leading up to the creation of the platformer sections of HE.
Dragon Arm effectively died when we decided to shut down Frozen Utopia. I doubt it will be back.
Jungle Bros ran into memory issues on the PCE, so lord_cack and I decided to try to bring it to the PC instead. We lost touch over time and the project basically faded into obscurity. I did release the code and assets to another PCE coder to see if he would pick up where we had left off but I am not sure if anything ever came of it.
Einzelganger was put on hold due to irl issues with its designer. We've since spoken about reviving the project in the future. Asteroid Challenge, a small minigame released for both PCE and PC-FX, was based on the Einzelganger game engine, and the code was later reworked for both LDP and the shooter portions of HE.
Also, that page has one minor issue... Henshin Engine isn't an Eponasoft project, it's a Saru Studio project.