Because existing in an arbitrary three-dimensional world is actually hard.

The hardware is quite expensive too - but that would be acceptable if a robot could do things humans do and didn't ask for breaks, sleep or a living wage. The main issue was that of capability. The humanoid robots simply aren't smart enough to do the tasks that would justify their existence.

Only recently did we get the tech to start emulating the more complex behaviors - and things like self-driving cars or humanoid robots that are actually useful start to look like they might be within reach.