Why aren’t swat teams and military squads ever useful in zombie apocalypse movies?

If there are any men here who are former or current military, or swat or any sort of armed force group, feel free to shed some light on the matter.

But in zombie movies, how simple is it for the government to just form a squad of a couple dozen soldiers or call in a helicopter and just mow down all the zombies?

Have some snipers up high, do some recon, call in a tank.

Im going off my call of duty knowledge but surely, it cant be that hard if your a bunch of armed soldiers or a swat team, against zombies? Right?