On the one hand it's true, there's no actually avoiding all the fallout, you will get exposed.
The thing is fallout isn't horribly and instantly deadly like, say, Coronavirus from an unmasked person is. You can be exposed to fallout and still be just fine, your body will heal from mild exposure and cleanse itself with time. Even a moderate dose may only make you sick for a time (granted an increased risk of cancer later in life but that beats the alternative). It's the really major heavy stuff right after a blast that's a lethal problem and a good rainstorm will hammer most of the heavy particulates out of the air promptly.
Edit: This is really funny, Grammarly suddenly rated my post as "Authoritative" the second I wrote that Coronavirus was deadly.