they continue to put many efforts on Flash fixs (seems that Flash it a top priority and then AIR).
Maybe there is a reason. I don't understand why.
To me, it doesn't seem that difficult to guess. At least until the Flash Player plugin is no longer officially supported, Adobe could be sued by other companies, if they did not take security issues seriously. Additionally, the tech press already loves pointing out the security flaws in Flash Player, so if Adobe didn't make fixing 0-days and things a top priority, they'd be getting a ton more bad press about a product that most of the company moved on from 5-6 years ago when they started focusing on Creative Cloud instead.
If executives and PR were dealing with the repercussions of breaches caused by unpatched security holes, I can assure you that AIR would have no chance of outliving Flash Player. As soon as the company made it through the storm, anything even remotely related to Flash would be killed.
In my opinion, these reasons are why Adobe made a big deal of out the 2020 announcement. They've basically warned everyone: We're giving you a little more time, but after this date, we're no longer responsible for this thing anymore.