It was a combination of the material factors and a mindset shift towards higher-level programming as the default. The appeal of CISC instruction sets when mark

It was a combination of the material factors and a mindset shift towards higher-level programming as the default. The appeal of CISC instruction sets when marketing to programmers lies in their batteries-included stance: they handle more of the binary encoding stuff for you, more of the math operations. With a RISC approach they have to write library code to do the same tasks, which adds some implementation complexity as well as potentially being most of the size of a short program. And that makes sense - if you expect direct instruction encoding to be the whole programming environment, which, for the first computers, it had to be. By the time you get to the microcomputer era the balance had shifted pretty resoundingly towards working at a higher level - that's why nearly every machine of that generation had a BASIC, and if you have a BASIC it's more important for the instruction set to be efficient, because efficiency becomes the only reason to drop down from a high level environment.