Ask yourself this, why should a guy work very hard to get an engineering licence and then let some unskilled person work on an aircraft ( reducing his income ) and then sign the work off, this exposes him to the risk that if something goes wrong the lawyers will come after him.
I know that you are all going to say that the engineer should only sign for what he has seen but the leagal profession will cloud the issue and insist that while an engineer has been called to inspect the engine he should have exercised his duty of care and seen the rudder hinge was about to fail.
No wonder the engineering company's want nothing to do with it !