In submersible tech, just beneath the surface is 0-30m depth basically (for salt water). Cellphones signals are about 2m max while higher frequencies (eg 2.4GHz) drop off exponentially so are <1m

Antennea can trivially extend over 30m, and can float on the surface. As a wire attached to an inflatable float, for either bidirectional communication or as a GPS beacon, or both, the complete solution could exist for less than $10k and less than 10 kilograms to solve this. Why doesn't this exist for this craft that can only be openned from the outside?? There exists the ability to communicate from directly above, so why can't it also communicate (further) through open air while bobbing near the surface?

You seem to be under the impression that the people paying a quarter million dollars to get bolted shut in an experimental sub to go see the titanic are reasonable and people who would think of that. They aren't.