I have very little prior experience with Unity, but was able to generate a map with trees, mountains and grass very quickly. Looked kinda crappy, but whatever.
I was hoping to implement some physics, that's where things went wonky, but I do believe that, give some time to go through tutorials, I should be able to sort it out.
There are FPS tutorials and templates available as well. Scripting seems pretty easy as well....again, one would have to have the time to figure it out, but, given a bit of prior design and programming knowledge, I think one could MAKE a credible Rust clone, for single player only, in the same amount of time people spend playing the game.
So, was just wondering why there are ONLY a few survival games out there, instead of hundreds?
So, I think the quick answer to your final question is that most people find more fun in playing a game rather than in creating one. People who create games aren't wizards, (it isn't a difficulty threshold) they're just people who have the right combination of desire and incentive to do so. For most people, trading time in the form of money for someone else to make the game, is a much more efficient way to enjoy them.