It’s not just remaining low level, the trend has been moving steadily toward lower level. The primary reason is performance. It’s hard to squeeze the best performance out of the high level APIs. Another reason is because the people who care the most and get involved in the API and standards committees are people who know the APIs and their limitations inside and out, and care deeply about performance; people like game engine render devs, browser developers, OS developers, and hardware developers. And so newcomers and the ease of learning these APIs aren’t well represented. On one hand, there’s a valid argument to be made that people can write wrapper libraries if they want easy-to-use libraries. On the other hand, some of us really miss how easy and fun using SGI’s GL library was before it turned into OpenGL.