You mentioned no motive or point of view taken by the collectors of this data. You said "compile data and provide general statistics"....Come on, nothing is so innocent. Data can and will be interpreted in many ways, also manipulated by filtering. focusing and selecting any subsets the researcher wants to use to make some point, and someone will make a point of something they find in the data and then it begins. Global warming is just such a controversy but let's not go there. Since you're looking for the "why not" instead of the "why" I would have to say that diving is a freedom I have that could be controlled in some way based on data collected from divers; e.g. my ascent rates, estimated blood gasses, depths and time there, pressure readings on surfacing, time in safety stops all could be used to justify some restriction or rule that inhibits that freedom. Or, could be used to get my ticket pulled. If someone determined that you actually could get a diver's data, that could justify creation of a law that says we'd have to provide it to some "authority". I don't want to download my driving data to the Police every day, why would I want to do the same with my diving data if it's used to control me in some way. Airline pilots do have their flight data and conversations (when they're awake) recorded and for good reason but I don't want that kind of scrutiny when I'm in the water for my recreation. That's the why not. This data certainly could be used for beneficial purposes as well but I agree with the other "Big Brother" sceptics here - stay out of my business!