However, when the 8087 was designed, RISC and VLIW processors were still in the future, because a fast cache memory allowing the execution of an instruction per clock cycle was still far too expensive in comparison with a microprogram ROM.
Most earlier floating-point accelerators were microprogrammed like 8087, with the microprograms stored in a ROM. However, there existed FPS AP-120B, introduced by the company Floating Point Systems in 1976. This was a floating-point accelerator for minicomputers, like DEC PDP-11 or VAX, which was marketed as a "supercomputer for the poor".
FPS AP-120B was a VLIW processor launched 7 years before the term "VLIW" was coined. This means that it was a horizontally microprogrammed processor (i.e. with multiple concurrent operations specified by each microinstruction), where the microprogram was not stored in a ROM, but it was fed into the accelerator by the host computer. Therefore the user could write directly such microprograms for it, to implement optimized computational algorithms.
Nevertheless, while FPS AP-120B was said to be a "supercomputer for the poor", "poor" was meant only in comparison with those who could afford to buy a Cray-1. Such a "cheap" array processor still had a price more than 100 times greater than an Intel 8087.
By the time when RISC and VLIW CPUs became fashionable, using microinstructions as simple as those of Intel 8087 for implementing floating-point operations was no longer acceptable, because having to execute tens or hundreds of simple instructions for each FP operation was deemed too slow. Therefore the instruction sets of RISC and VLIW CPUs were eventually extended to include FP operations as single instructions, which had to be implemented in complex hardware in order to achieve an execution throughput of one instruction per clock cycle.
It's a question of throughput that can be extended cheaply enough.