I thought they did provide seats to suit Mr & Mrs average, which will relate to the cost of that seat.
Now if YOU are a fat bloke, then YOU should pay extra for a fat guy size seat, which there are on 99% of flights.....
Or would you like a more expensive cattle class seat to fit YOUR size and give a reduction to average size folk....?
Sounds rather complicated to me, so it's all down to YOUR size paying extra in posh class, sorry about that...........