Why do you think everyone is so hell-bent on developing the "humanoid" form robot? Do you think it is just the WOW factor? I mean it is cool, no doubt but it just does not seam very economical. I mean there is no reason Optimus needs a head. They could mount the cameras just about anywhere or everywhere and have a 360 degree view, for example.
Maybe once they get past the WOW they will get on to more purpose built robots?
Well not everyone is developing a humanoid. There are other robots being worked upon.
But the answer to your question is robots, especially if they are mobile, have to operate in a world that was developed for humans. Thus having the human structure is vital. We are bipedal beings that constructed a world around it. This is how the general purpose bots can fit in.
As for the head, there is a reason: humans. Having a bunch of machines running around without heads and a camera like you say would freak people out. So for comfort, that is place there although there isnt really much need.
I think you will find they have a purpose very soon. My guess is we see use cases rolling out in the next 12-18 months.