Isn't it easier just to unfasten them?

Yes it is -
Unless you are hanging upside down, disoriented, unable to see . . .

Sorry, Tony, I just don't find that persuasive. If you're "hanging
upside down, disoriented, unable to see," you're going to have a lot
more trouble finding your tool, unhooking it from your belt, etc.,
than opening a seat belt buckle you've done hundreds of times before.

vince norris