When memory bandwidth was not the bottleneck, it was a good idea. That plus the earlier period in VLSI when there was an extreme premium on the number of gates

When memory bandwidth was not the bottleneck, it was a good idea. That plus the earlier period in VLSI when there was an extreme premium on the number of gates you put on a single die. If you could fit an entire simplified CPU on a small die you could win big, and this advantage continued as FPUs, cache, and more and more cache were added. Nowadays gates aren't exactly free, but dies are constrained by other considerations like power and size (yield) balanced against what more gates will gain you. Outside of tiny microcontrollers, I don't think any one is obsessing over the issues that limited the 1978 8086 to 29,000 transistors, or the 1979 68000 to 68,000 (https://en.wikipedia.org/wiki/Transistor_count https://en.wikipedia.org/wiki/Transistor_count).