The whole point of Voodoo 1 was making it as simple and cheap as possible by removing all the advanced features and calculating geometry/lighting on the CPU.
Later SGI Geometry Engines used custom, very specialized DSP-like processors, but the microcode for those were written by SGI, and not end-user programmable.
There were probably research systems before it, but AFAIK the Geforce 3 was the first (highly limited) programmable geometry processor that was generally commercially available.
AI Accelerators have been a thing for decades - DSPs were used as neural network accelerators in the early 90s - and Cell processors were a thing by 2001.
GPUs just became vastly more accessible to general purpose program in the last decade. People were doing it back in the 90s but it was seriously hard.
We finally hit a tipping point where it's just kinda hard.