It's not so much about functionality as it is about available assets. RPGM already has a wide range of assets available, so I don't have to build the game from scratch like I would with Ren'Py. Since these are just side projects, I can develop them quickly while waiting for our artist to finish the drawings for the main game. Plus I actually spend a lot of money on the main game just for some assets like backgrounds and stuff. If people hate moving their characters, I can just make the game moving automatically so they can just click on the dialogues like they'd do in renpy.