Earlier quoted context omitted.
They can, but since the data is very noisy the 3D reconstruction is usually not very good. If you actually need to measure something, analysing the 2D images is much more precise. EDIT: Also, it's really hard to visualise density in a 3D view.
I just don't see what harm there is in making unregulated devices even if they're hard to interpret and less acurate.
The problem with 3D reconstruction being difficult has nothing to do with wether devices are regulated ornot.
Also,noone is stopping you from making a DIY ultrasound and selling it to enthusiasts.