When will indie devs stop making only low-effort horror games, roguelikes, and games made with rpgmaker?
Easy: when the tools to make a more complex game of their choice are easier to understand to the layperson and when trends change.
Why are there so many games made on RPG Maker or Unity? Because they're cheap or free with cheap and free assets, and a library of other people's code and programs that can cut the heavy lifting in half for you.
Why are roguelikes and other random generators a thing? Because you don't have to spend as much time with asset creation, balance (if you market it as hard for the wrong reasons), or level design.
Why low effort horror games and walking sims and visual novels? Because they require low amounts effort, time, and money that is attractive to smaller game companies who can't make shit back. They also function as a low rent way to make a shitty movie or comic without having to draw or film either.
Lastly, some things are just trends. If you have no money but want money, why not follow something that has an audience hungry for more? For a while, the indie platformer with artsy story/visuals was popular due to the popularity of Braid, Limbo, Fez, etc. The "Simulator" genre became a thing when Surgeon and Goat Simulator got popular. FNAF clones littered the shelves for a while. Battle royal had it's clones come up and then die. We're going to get a wave of boomer shooters now I believe, that's the trend I've been seeing recently.
There are still a good number of indie devs & indie dev teams who aren't massive hacks, children, pretentious art students, or hobbyist playing around, they're just harder to find unless you go looking for them. We won't stop getting low effort shit made by talentless people on the same 3 engines for the same reason Deviantart will always have shitty MSPaint and lined paper and pencil art of the top 5 fandoms and fetishes: it's all easily accessible and anyone can do it.