Because they are the primary character. To me this is a no brainer-the heroes of the story get to do the heroic thing. They exist in a elevated reality that realistically would not occur in real life. One of my top 10 shows is J*A*G, a show about a former naval aviator turned lawyer who still goes toe to toe with SEALs, terrorists and the like. He survives a lot of things that realistically he probably shouldn't or at least would be drummed out of the US NAVY for. Same with MASH and all other protagonists that I watch.There's literally a TNG episode where Picard flies outside in a shuttle to guide the D through some kind of time/gravity distortions.
Which is why Discovery get flak for Burnham makes about as much sense as being made that the sky is blue. Protagonists always exist at a higher level, get tapped for the biggest projects, and do the most dangerous stunts that should kill them but at the last second they pull it off. In other words,
(start video at 0:41)