Because then you can only use that instruction if you're sure the target CPU supports it... or else your program will crash. Sequences like "or r1, r1, r1" are

Because then you can only use that instruction if you're sure the target CPU supports it... or else your program will crash. Sequences like "or r1, r1, r1" are going to be harmless when run on a processor that is unaware of its special meaning, which is exactly what you want for a "hint" instruction.