I dont like Ren'py, its just a slide show not a game.
If i wanted a image slide i just extract the images.
I agree that Ren'py games can feel like slideshows IF the creator wishes them to be so. However, the beauty of Ren'py is that the creator also has the flexibility to make fully fledged games just like RPGM games are.
However, the main appeal of Ren'py games is that they save you the hassle of having to spend so much time just needlessly traveling between locations, giving you time to actually enjoy the narrative of the game rather than have to wait sometimes a considerable amount of time between scenes.
That and the ability to save at any given point gives you the option to quickly test all the different outcomes without needing to start over from what can be a much older point in the game, saving you a lot of time that you sometimes don't have.
Now you may not want any of that which is fine, but others do and it's good to have options should you need them, rather than be stuck with the way RPGM games force you to play.
So in Lily of the valley's case, if I now decide to start the game over I would have to spend hours just going back and forth between locations, when all I care about are the interesting scenes in the game. But had the game been Ren'py instead, I would have the option to just skip anything that I personally don't care about and focus on the parts that interest me. Wouldn't it be nice to have that option when you need it?
That's just a very brief explanation as to why many of us prefer Ren'py games, they're simply much more convenient and flexible.