> But don’t all pilots have to lodge their flight plans?

No, they don't. And many municipal airports aren't even manned and, outside of certain areas, aren't under direct air traffic control. I flew in a Cessna with a private pilot who landed at a municipal airport in Los Angeles Country without ever talking to anyone. He just announced his intention to land on the published radio frequency, received no objection (because no one else was around), visually confirmed the runway was clear with a flyby, then lined up on the approach path and landed. I got the sense this is the norm in civil aviation outside of major airports.