Security
I think you have got it right. As an SLF frequent flyer living abroad I long ago gave up landing at a UK airport to then catch a domestic flight to my final destination, as the security hassle from the UK security staff is just too much to stand, especially coming in on an LH flight.
I now ensure I land at a continental hub and make my final connection from there. I will even accept a landing at CDG before a landing at LHR or Stansted