I'm sorry but you have much to learn.
https://www.businessinsider.com/a-close-look-at-f-16s-performing-strafing-runs-2016-3
If you open this link. You will find an aviation photographer talking about two F-16C's from 510 FS doing strafing runs over a deserted Air Force base somewhere in Nevada. This mission was part of Red Flag. The jets were routinely flying below 500 ft.
However, What you're saying is;
1) Cannon has no role in A2G against airbases/ground targets
2) Cannon is the last resort if an aircraft runs out of missiles
3) Cannons are a stupid idea to use against foot soldiers.
However, large scale and supposedly REALISTIC warfighting scenarios (red flags) show us that cannons are still very much relevant and preferred once the airspace is threat free (against low value ground targets).
In ACES 2018, we saw Turkish F-16 pilots teaching our F-16 pilots skills of urban warfighting with M61 Vulcan cannon as a preferred mode of attack. Dont take my word for it. But ASK SOMEONE FOR GOD SAKE instead of preferring your own strongly formed opinion.
In July 2016, we saw Turkish rogue F-16s firing cannons over police stations and other ground targets during Turkish Coup. Google it!
ISAC is no different. And I'm glad our Air Force knows best.