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.
No, in a disputed territory there's one reality, and 1..n delusions.
If you bothered to actually travel to Ukraine you'd find there are plenty of places where you can get dronestruck by either side. If you bothered to actually travel to the disputed India/China/Pakistan border area you'll find either side might hit you with a stick and take you into custody. If you'd lived in Northern Ireland 40 years ago, or even South Italy today, you'd find that the group that enforces its laws with force in your street might be quite different from the group that is internationally thought to be "in control" of the country you're supposedly part of.
Control is not a binary. There's no country in the world that doesn't have murders, kidnappings, and takeovers. When (as in South Korea recently) there's a group of people outside a guy's house who say they're coming to arrest him under a warrant from the Supreme Court, and he says he's the President and the warrant is illegitimate and they're just a gang of thugs trying to kidnap him, who is in control? There's no way to answer that except retrospectively. When armed men declare independence or a revolution, are they "in control" of an area in a sense that should be shown on a map, or just regular criminals? Again, no way to tell.
I'm quite familiar with Taiwan thank you very much, and yes it's one of the more stable situations (although these things have a way of seeming stable until they suddenly aren't) where one of the claims is rather attenuated and silly. That doesn't mean there's a simple, easy solution to territory disputes in general.