Why is it not possible to keep the masks made in Camera RAW or import them as photoshop layers?

I thought of that workaround too, but it is still cumbersome. I felt I was quicker with the quick selection tools, but that is pretty much doing the same work as in Camera raw... 

Like I said; that would require a major rewrite of ACR. It's not a matter of 'just' changing a few lines of code. Maybe Adobe will do that one day, AFAIK you are not the first person who suggested this.

What you've just described would require layer support.

As a work around take the raw image into Photoshop as a smart object. Then open the SO and make an extreme adjustment using the camera raw mask - for example turn everything in the mask black and everything outside white. Then you can use that output to make a selection/mask in Photoshop and save it as a channel. Then go back into the SO and undo the extreme adjustments.

Dave

Camera Raw doesn't need to work with layers. It just needs to export an amount of images with the contents masked out corresponding to the amount of masks and preferably put those images in one layered file.

Camera Raw does not support layers, so it cannot send out a masked (= layered) image to Photoshop. It would require a major rewrite of Camera Raw, so that is why this is not possible (yet?). It would be nice, though.