It is also the simplest and most widely available one[0], working from decades old PCs to whatever is latest one, not only from the official drivers but also 3rd party implementations[1] that target other lower level APIs for environments where there isn't an official implementation.
[0] on open platforms at least
[1] it most likely wont be a 100% compliant one (even SGI had trouble on that front :-P) but in practice it'd be usable