Because it's designed to be hard to execute on anything that is not a CPU.

Right, but the program is generated by the miner. So the miner could just generate a program that has no branching, and run it on a GPU.

	▲	tardedmeme an hour ago \| parent [-]
		Each program is guaranteed to have a certain number of certain types of instructions, such as (IIRC) exactly one divide instruction.