There's probably a lot of RPGMaker games that are not successful too.

I think it's unusual for the first few iterations of a drastically original idea to get it right. When you look at modern design sensibilities in almost any genre, they're usually quite sophisticated compared to early attempts. People play hundreds of hours of a fighting game, slowly figuring out what was balanced and what wasn't, whether there's degenerate states like unbeatable combos, etc. They discover the moments that are addictive, and the ones that make you want to quit. That knowledge then feeds into later games, things like heuristics for how to trade-off speed and damage or how to allow complex combos without them taking over completely.

The further afield you go, the more you need to discover, the fewer existing genre lessons that are applicable to your work. Hopefully you create something that showcases the great idea, but probably without the sophistication for mass market appeal. Other developers see what you were going for and refine, your players figure out the nuances of your system and critique them, eventually it becomes something that can be a AAA hit, although at that point it's no longer original.

RPGMaker codifies a lot of accumulated knowledge about the core RPG mechanisms of combat, stat progression, loot, etc. There are highly polished RPG's for developers to base their work off of. At that point, it's more probable that a cookie-cutter game hit all the fun notes then an original one.

That said, the original one can have a lot bigger long term impact on gaming even if it isn't a hit.

RPGs are super dupper content heavy projects, developing contents costs a lot of time, rpg maker probably have the most massive free to use content database, so for many indie projects its like the only option.

Ive been wanting to develop a post apocalyptic rpg since I got to game developing, towns, races, equipped itens, weapons, combat animations... I dont even dare to try, doesnt matter how much I try to simplify it in my head (simplify while keeping it to my interest), it would be still too much stuff to put in. So it makes sense to see lots of RPG maker stuff around (although Id never use it myself, I also like being original).

"Good" and "original" are very different things which may or may not overlap in a particular game. I've loved derivative games that were perfectly executed and hated very original games that were poorly done. A truly original game that offers a new sort of experience will be interesting, at a minimum, but that alone doesn't mean it will please players or reviewers because novelty isn't everything.

Sometimes people just have a story they want to tell or a creative itch that they need scratched. If RPG maker is a sufficient tool to make that happen then why not use it?

Personally, that I'm unlikely to play games in this style, whether RPG Maker was used or not, I think comes from that I've saved the world enough times in my life and I just can't conjure up the patience to get passed the initial exposition and tutorials anymore. I kinda need to be hooked early on or otherwise be convinced that it's worth my time to play. I probably miss out on a lot of good stuff.