I think that maybe it's because Onavo acquired the information with a specific agreement with it's users, which didn't cover the way Facebook used it after FB a

I think that maybe it's because Onavo acquired the information with a specific agreement with it's users, which didn't cover the way Facebook used it after FB acquired the agency, but then again, I'm not sure. SOP for these situations is to license the data from the agency, so you can say that you're using third-party data which is also available to your competition. Level playing field and all that. Acquiring the entire company is a risk because it closes it off to competition and isn't necessary to just use the data.