The cabin is meant to be exclusive, which means that the people who pay a substantial for the service expect a bit of peace and quiet, not to have everyone trailing through.
Oh come off it. Half of the people in there have their seat paid for by their company and take pleasure in looking down their nose at "ordinary" passengers.
Whilst I can understand the benefit of paying extra on long haul (and indeed I generally do pay extra) for some peace and quiet, this kind of snobbery has no place in the modern short-haul market.