Two answers:
1) They don't, and that's not what the buoys/drones are collecting, or
2) NOAA collects comprehensive oceanographic data all over the world, to track El Nino, or global warming, or fishery-affecting pollution.
The real answer, of course, is that I don't know, and nobody is telling us.
I know because I was an ASW(think sonar) officer in the Navy.
Because salinity and temperature data at different depths let you know where to place submarines. It is perfectly legal to collect such data in international waters, however armed theft is not.
The reason you need to collect such data in peace time is that it is to late to collect it in war time.
Somthing that has drawn very close due to our current president being more interested in sexual preference than world affairs for eight years.