I agree with RF in a way, when I started, pubs wouldnt get a music and dance license if wired in T+E, I recall a right scene once when someone spurred a T+E off a pyro ring main, they were threatened to be shut down till it was sorted and in comercial it was rare to even see T+E anywhere, one of the main reasons metal was used, I suppose was to ease terminating, pyro, conduit , swa Etc.
The recent influx of plastic seemed to start when people opted for T+E, FP and YY flex instals, same as the demise of Bus bar chambers and metal switchfused submains, being replaced with MCB supplies with little discrimanation, in my view standards have gone downhill and i dont feel its just Domestic contracters and also people dont tend to want to pay out for quality.