People who bring up Monster 3D keep forgetting that 3dfx died when they were unable to compete with robust implementations of D3D and OpenGL (proper OpenGL support, not just GLQuake).
I don't think that's accurate at all. Voodoo worked fine with Direct3D.
3Dfx died because they over-reached. They bought a company and got into the board-making business, not content with just making GPUs. Then they over-promised and under-delivered in the Voodoo 5/6 era. This was at the same time nVidia was gaining strength.
Questionable choices sunk them. nVidia bet on hardware transform & lighting, letting the GPU do more complex tasks, even if it burdened it a bit. 3Dfx bet on cinematics like the T-Buffer, motion blur, etc.
What all that has to do with the emergence of physics processors I don't know.