We did.
10+ years ago, every GPU manufacturer had its own low-level API. OpenGL was only unifying API, but it was slow and underdeveloped. Then, when developers begged for salvation [each game had to support crapton of APIs], Microsoft came and delivered DX. It was slower, but after few versions it got better [DX6/7 and up].
Now when only 2 big GPU manufacturers are alive, and majority of AAA gaming was moved to consoles where low level APIs never left, developers want to bring fast APIs back to PC. They asked for it, AMD delivered with Mantle.
Hopefully Nvidia will adopt it also. AMD confirmed that Mantle can be adapted for other modern GPU ahitectures from their competition. Mantle is not coding to the metal, it is still using slim abstraction layer for talking with brand new small GPU driver.