It's simple, in part, because it only operates on registers and immediate values, so there's no chance of it taking a page fault. That makes it easy to pipeline

It's simple, in part, because it only operates on registers and immediate values, so there's no chance of it taking a page fault. That makes it easy to pipeline, and, compared to having to save a lot of ALU state after a fault, the operation this opcode performs is, indeed, fairly simple.