I don't quite believe the reason about guns not being fast enough to bring it down. Enough bullets will shred it eventually and bring it down pretty fast.
More of an issue would be that the plane has to come too close to the (relatively speaking) stationary target. That would be dangerous for the pilot and the plane.
Well, unsurprisingly, the US military knows more about this than you.
Multiple planes and over a thousand rounds is not enough to bring down a much smaller balloon[1]. Not to mention, a leaky balloon will fall slowly, making it an obstacle for regular air traffic.
A single missile is faster, cheaper, easier, etc. We didn't want to bring the balloon down "eventually". We wanted to bring down the balloon precisely and immediately, once it was over water but still in US airspace.
> I don't quite believe the reason about guns not being fast enough to bring it down.
What makes this reason a challenge for you to believe?
The F-22’s M61A2 20mm Gatling gun propels 20mm (~0.75”) rounds. A full load out is 480 rounds.
The target is a 90’ diameter, nearly atmosphere equalized pressure vessel. Striking the target with 480 rounds of that size is nowhere near enough to create a large escape surface for the slightly positive pressure gas to vacate quickly.
More of an issue would be that the plane has to come too close to the (relatively speaking) stationary target. That would be dangerous for the pilot and the plane.