I had been watching DirectFB development very close back in early 2000-s. As far as I remember:
1) It uses Linux FB support for modesetting. So no multiple monitors, rotation, etc.
2) It has its own input stack.
3) It required custom kernel modules and direct hardware access from the userspace (ugh).
I don't remember it ever trying to support OpenGL, but I guess that blitting from a texture to framebuffer is not that complex to add if you have a working EGL.
In short, DirectFB is more like a classic framebuffer with several hardware accelerated operations. It's not nearly enough for modern graphics.