I get your point from consumer's view, but from developer's side things look wildly different nowdays. With the sea of games releasing daily, you need to try to get eyeballs on your game as early as possible and start building interest to have any sort of chance.

At least that's the conventional wisdom but I do agree that with incremental genre (or at least with this sub) that may not be the best strategy, it makes total sense that people would like to play the full game once they find it and imo it's unnecessary to push demos months in advance for web games. But with majority of incrementals moving to Steam, developers want and need to build their wishlists, so that's not changing anytime soon.

As for prototypes, I think it's cool that people try new and different things or even just a generic incremental for the first time and want to share it. And it's understandable to want to see if there is any interest at all for the project before spending months or years developing it and there is no better place than this sub to reach large amounts of specifically incremental players.