Wow. I apologize for the dumb suggestions. My Jeep does the same, except if you leave the key in the vehicle it doesn't honk, so that's the difference. I assumed it worked the same way with the Ford. There are plenty of times I want the engine running while I'm out of the vehicle. A very simple example, as stated, is opening a gate, but something I do routinely is air up my tires. You're supposed to have the vehicle running while the compressor is running. You can't go from tire to tire while in the rig.
There have got to be hundreds of other reasons for having the engine running while checking something, turn indicators working, backing to hook up a trailer and getting out to check things (yeah, there's a camera...I know), but that seems like one of the dumbest things a car manufacturer would do.
2022 Jeep JLR, manual with even more extra guacamole
Sold - 2021 Jeep JLR, manual w/extra guacamole