<i>When memory bandwidth was not the bottleneck, it was a good idea.</i><p>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.<p>Nowadays gates aren&#x27;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&#x27;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 (<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Transistor_count" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Transistor_count</a>).