It doesn't make sense to make all data public when there might be something the FIA or other teams didn't know about and might be useful in the future.
F1 is all about living on the edge of what's allowed by the rules, and more often than not crossing that line and hoping not to get caught by the FIA. There's a fantastic interview with Ecclestone, Withing and Piquet (1) where they reminisce the olden days and have a laugh admitting their Brabham car was so illegal they would have been disqualified by the FIA had they knew that. 2019 Ferrari had an amazing engine and then they got caught doing tricks with the fuel sensors.