The usual (and suboptimal) solution to that one is to just use the biggest airport in the metro area -- e.g. servers in Chicago are tagged ORD even if they happen to be located next door to Midway.
However, IATA does provide city codes even if no airport in that city actually uses them. London's is LON, Chicago's is CHI. It's better to just use those.
Same. Biggest airport in the area unless the data center is somehow VERY close to a secondary airport or something.
Can't speak to others but one of the main reasons is if our team has to fly chances are they're hitting the main airport, anyway. Like, we're not going to try to finagle a Spirit or RyanAir flight, just fly to ORD and taxi / uber. For someone looking to travel on the cheap and with no concerns about time those airlines and airports are fine, but work demands change that math.
However, IATA does provide city codes even if no airport in that city actually uses them. London's is LON, Chicago's is CHI. It's better to just use those.