Runway restrictions
I dont pretend to know the regulations restricting aircraft usage, but if you look at LCY it started with Dash 7's and gradually chipped away with the regulations with safety cases and trial flights.
30 years on modern aircraft have different performances, with "short packs" etc.
Long gone are the days when the old BOAC had to find a new aircraft i.e. VC10 which were needed to land at "old empire" short runways.
It seems now you make the aircraft fit the runway and not the other way around.
Not an exact science but food for thought.