Good answer. I'll also point out that RAM was expensive in the olden days, so you wanted your instructions to be as dense as possible. It made sense to have one

Good answer. I'll also point out that RAM was expensive in the olden days, so you wanted your instructions to be as dense as possible. It made sense to have one instruction do as much as possible. It also made sense to have instruction lengths ranging from 1 byte to 4 bytes or more like the 8086, even though that made decoding complicated. Also, for the original question, you really don't want to program in microcode directly, as it's kind of a mess. Micro-instructions expose a lot of ugly hardware details. Moreover, it locks you into a fixed architecture and you can't upgrade, because the microcode will change.