As someone who actually works in the game development industry, I find it funny how people think these ideas haven't been made yet.

The real challenge with making these things is getting and organizing a team to do it, as well as pay the people enough to get the job done. Big companies don't like investing in risky out-of-nowhere ideas, and the indy companies that are willing to try the weird ideas don't have the funds to do it right most of the time. 

Also, it's interesting to see how much people underestimate the work involved in some of the ideas they suggest.