Why can't you use a spacer with a dry powder inhaler?

I've tried looking for the answer to this and just couldn't find it.Why can't you use a spacer with a dry powder inhaler?
because the powder would hit the surface of the tube and just drop off leaving them there and not in your lungs.Why can't you use a spacer with a dry powder inhaler?
Additionally, the design of the spacer is not conducive to the DPI.