Inglebyboro,
Unfortunately you picked just about the worst airport in the world for efficient passenger handling. Manchester probably did send the request but there was no way anyone in Rome was ever going to read it, let alone respond to it.
When the football was on a few months ago, the turnround took several hours because all the handlers simply evaporated. With that kind of attitude, your pre-allocated seats are hardly going to interest anyone.
Despite this, Jet2 and its crews do their very best to serve this difficult route as best they can and the average end-result isn't too bad. You won't find many Kens in EZY or Ryanair.