On the same note.
Stuff glorifying police or army have historically figured far more in authoritarian and totalitarian imagery, and those narratives glorify the brave human risking life and limb for victory and stress their vulnerability and mortality.
So I think the main reasons superheroes eschew that baggage is...they don't exist and can't exist for the most part. We aren't in danger of someone getting powers from yellow sun radiation, a radioactive spider, a Green Lantern ring. That stuff can't happen in the real world.
When Spider-Man failed to save Gwen Stacy...it was done in a way that was over-the-top, a goblin drops a blonde by ramming her off the bridge with his glider. That's not the same thing as say if Goblin killed Gwen, and others, by wearing a mask and taking guns and walking into a cafeteria and gunning up everyone. The former is a death staged in the comic book imagery and landscape, the latter has a visceral familarity to us that hits close to home.
That said, there are superheroes who are problematic. The Punisher has been co-opted by real world "thin blue line" type cops. In the case of Batman and Iron Man, their civilian alter-egos billionaire playboys both of them are essentially propaganda for untaxed inherited wealth and accumulation. Tony Stark is virtually a one-man military-industrial complex and his entire narrative in the comics and MCU is a way to limbo under the implications of such a character as a moral icon.