Probably because the robustness of the box makes it very dense. You could still encase the dense package in foam but that would make it very voluminous. It would still need to be in a location and with a mounting system to insure it breaks free from the main body of the wreck if it's under water. A pinger with a 30-day power supply is probably considered more practical.
Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.
Albert Einstein
Albert Einstein
