You'd also be essentially legitimising the right of conquest if as soon as country A invades country B you move the border on the map. That would be pretty counterproductive.
Documenting reality doesn't endorse what happened. Istanbul was Constantinople. Shit happens. If I'm travelling, I'd much rather the flags and borders reflect the situation on the ground instead of making meaningless humanitarian gestures.
The issue is reality not being settled or agreed upon. For disputed territories there is effectively two realities both officially backed by sovereign countries.
You can come up with some arbitrary criteria to split the difference, but your reality would break when you effectively set foot in a spot that works under the competing assumption.
