Why are some airports so far from the city they are named after?
Because airports need an enormous amount of flat land, generate noise nobody wants nearby, and — in some cases — because the name is a marketing decision rather than a geographical description.
The genuine constraints:
Land area. A major airport needs runways of several kilometres plus terminals, taxiways, cargo, fuel storage and parking. That much contiguous flat land is unavailable near an established city centre at any price.
Noise and safety zones. Development is restricted under approach and departure paths, so airports are placed where fewer people are affected — and cities then grow toward them, producing the noise conflicts that surround most older airports.
Obstacle clearance. Approaches must be free of terrain and tall structures.
Room to expand, which is why new airports are built further out than currently necessary.
Historical accident. Many airports began as wartime airfields or grass strips outside what was then the city, and the city subsequently moved.
The naming practice, which is the part travellers find misleading. Some airports are named after a major city they are nowhere near — frequently an hour or more away, sometimes closer to a different city entirely. The practice became widespread with low-cost carriers, for whom a secondary airport's low charges were decisive and the marketable name was worth more than the accuracy.
The regulatory response. EU rules have required that the actual airport be identified clearly at booking, precisely because passengers were arriving substantially further from their destination than expected.
Why it matters practically:
Total journey time and cost must include the transfer, which can eliminate the fare saving entirely.
Last transfers run early. A cheap late-arriving flight can strand you if the coach or train has finished for the night.
Two airports "serving" a city can be on opposite sides, so a connection between them is impractical.
Check the three-letter airport code rather than the city name, since the code is unambiguous.
The counterexamples — city airports genuinely close to the centre — exist where geography allowed it and are prized for exactly that reason, usually at the cost of short runways limiting which aircraft can use them.