Yes this was my reaction too, I can't see any reason to have the airtag on the outside at all.

Kindred spirit! My old Apple Watch is at the bottom of the Colorado River near Moab. Still paired in Find My.

It was a pair of scuba tanks in a custom bag which was too small for the tanks, so there was no really secure inside.

But, it was attached to the handles with one of these: https://www.amazon.com/dp/B0B34Y5YZS

There are people who dive down and find lost stuff on the bottom of lakes, and people who go magnet fishing, they still might find your keys!