It is because the DEV focus on one update each for the paths on the same game file. What you finished in the RPGM is at the end of that update, and was suppose to keep going There is more free roaming and freedom to interact with in game mechanics with RPGM. However RPGM has a limit to its system and will eventually cap. Adding more stuff on eventually makes the game unstable and not manageable. Since DEV fuse all three paths, the RPGM system capped as the files got bigger. Honestly DEV should of create three separate RPGM game file calling each what it is, cheating, cuckold, and blackmail all with the same prolog. Should DEV cap, he can then create a new RPGM game files as part two or continuation and go from there. Or DEV could simply just create a new RPGM called SHADOW OF DESIRE 2 and repeat the three in game paths with a small prolog that ties things together as a intro, and simply branch off back into the three separate paths. But at last DEV went the other route.
Due to this the DEV move over to REN PY where it is easier to manage, and what do you guess start from scratch taking bits of the plot from the original RPGM. In REN PY he can focus strictly on story, art, renders and do not have to manage the in game mechanics of the RPGM. Since RPGM requires a lot of work. You lose the free roaming, game mechanics and suspense aspect of guessing out things for yourself while playing in game. But in turn you get faster update, more visual novel, animations, drastically improved arts, and point and click to move the plot forward. You also finish the game faster as there is nothing to do but point, click, and read. I preferred the RPGM but I do understand that it requires more works. Other just want to click and read. You make that call for yourself once you get into the REN PY updates.