Because you can never be certain that the ham will NOT
ever build anything. Additionally, all hams have technical
responsibility for their stations and the RF signals they
transmit.


If the FCC is to trust us with the legal ability to
pop the covers off our transmitters and make
adjustments and modifications, we need to have passed
tests to show that we have basic knowledge of RF and
such. That we'd know how to run and maintain a clean
operation.

It's quite rare that the FCC busts a ham for faulty
equipment anymore.