Because it's the law.
A mile from the airport isn't that far. I'm a couple miles from the airport and my ceiling is 300 feet IF I get temporary approval to fly here at all.
https://app.autopylot.io/#/map
Find out if you're restricted below 400'
Just curious why 400 feet. My area is flat, nothing above 60 foot telephone poles. I'm about a mille from an airport and helicopters fly over a lot. They are supposed to stay above 500 feet but I think they sometimes dip below that, so I usually...