I mean, threatening legal action against a multinational media empire is much harder than threatening legal action against a handful of independent programmers. Not saying it's remotely fair, but that's just how it is.

Game mechanics and general art "styles" aren't copyrightable. Game characters, music, and direct art assets are.

That's why, for example, "Fighting is Magic" got shut down by Hasbro while "Them's Fighting Herds"--the same game with different skins, music, and backgrounds--can't be (and why Hasbro has no interest in shutting it down).

So you can go out and make an adventure game where and elf boy gets a magic sword and saves an elf princess from a demon lord. Just not a "Zelda" game specifically.