Those standards are interesting, but I think hard to enforce on all the apps. I don’t have any stats on this but my gut feeling is that most of the authors of apps on F-Droid don’t get any money from their work on those apps. Features and updates depend on their time available to improve their app, but enforcing rules like these imply a lot of work.
Besides, forcing an app to be updated every 6 months doesn’t necessarily make sense, for instance a flashlight app doesn’t need any update.
Forcing a backup feature with encryption is not a trivial task, and would require a lot of work to ensure it works in all cases properly.
I agree completely that we need to strive for better programming, but in my point of view, forcing those standard would drive developers away from F-Droid.