Well the primary reasons for not much progress after 5 years are:
1. He rebuilt the entire game map / level, three times. First was a linear experience, focusing on quick action, no puzzle solving and limited platforming. Second was a procedurally generated experience with randomized sections. Third is the current incarnation, of another linear experience but heavy on puzzle solving and platforming.
2. He rebuilt how spells are cast, three times. First was a simple point and blast spell system. Second was a more involved spell wheel, but was still in some ways simple enough to understand. Third is the current incarnation, where it is very involved, needlessly complex and requires drawing the spell to cast it; I personally hate this system.
3. He rebuilt your basic attack, three times. First was a simple magic bolt that you fired from your fingertips at low mana/when no spell was selected. Second, was a dagger that replaced it. Third, is a more involved dagger attack (not sure the point as spells are the main focus) and the really shitty 6 shooter pistol, which feels totally out of place.
4. He rebuilt the charm system, four times. First was a simple, aim at a target and hit e once, to charm them and then they would follow or attack enemies for you, or you could click them to have sex. Second was a QTE click fest, where you hit E a lot to slowly charm them and of course getting attacked totally interrupts this. Third was a charm cloud, that sometimes charmed enemies and sometimes they totally ignored it. Fourth is the current incarnation.
5. He added in some cool spells, spent a lot of time on making them useful, and then took most of them away. Current spells are of course much "flashier" but overall we have lost a lot of interesting spells.
Then of course there is the issue of working on animations for an enemy type, then removing them from the game (ie tentacles, the giant, the fish people, and plants). Or redesigning the movement system heavily; like you used to be able to climb objects back in the procedural generation build... can't do that anymore. Or redesigning the patreon sandbox map, several times.
Honestly the guy is a pro at wasting time. If he had stuck with the first incarnation of each game system, the game would be pretty much finished at this point. But no, he has to rebuild everything from scratch every 12-18 months, which negates all of that progress during that time. Maybe it will pay off in the future, but thus far, I don't see him getting finished anytime soon. Like seriously, UE6 will be out sooner than this game will get finished if he keeps "redesigning the wheel".