It's not necessarily the airport themselves that comes up with these nonsense excessive check-in times, travel agents can do the same, quite independently. Yes, I know nobody uses these for their own travel nowadays, but I come into contact with one or two who arrange business travel.
One we used sent me an e-mail listing my departure from London City at 0700, and stating that as it was an "International" flight I needed to check in a minimum of 2½ hours before departure. When I pointed out that this was long before the terminal building was physically unlocked in the morning, I was told that it was a "necessary standard". When I then asked what part of any necessary standard involved their customer standing outside in the winter darkness for the best part of an hour waiting for the terminal doors to be opened, there was of course blankness.
And it's not just check-in times, many airport FIDS will progress from Go To Gate, through Boarding, to Closing, you see people leaving meals half eaten in the restaurant, and when they rush to get there they find that the incoming aircraft is not even on stand yet and everyone is still hanging about; London Stansted is a particular offender here.
Those of you who are Dispatchers and complain about passengers turning up late at the gate, and similar, may care to look at your own airport procedures and wonder whether, having cried "Wolf" for far too many times, it is any surprise that the pax, having had so much of their time needlessly squandered previously, take no notice of instructions any longer.