In its early days, OpenGL benefited in many ways from being a "forward-looking" API that exposed far more functionality than was implemented by graphics hardware. Software that used those features got faster throughout the 90s with no rewriting needed as that functionality became available on GPUs. (Of course, software like games that wanted to be fast now just avoided those features.) When graphics hardware started to include features that hadn't been anticipated in OpenGL, things got messy and stayed messy.

Now that the feature set of graphics hardware is very stable and uniform across different vendors' hardware, the APIs are needed to solve an entirely different problem from what they were invented to do.