In real life at gatwick all planes you this runway as a taxiway when taking to or from runway depending which end is in use.
However when i was there on advanced taxing down it as we do in real life i got told this is to a taxiway please vacate runway. I nearly got ghosted for doing something which is true when he was telling me to do a wring thing.
It’s been raised before, and I have made the same point as you
In real life isn’t isn’t treated as a live runway and you don’t need to get permission to enter or cross it. However, I can see the issue in IF being that most people won’t know this so best treat it as a runway in order to keep things simple.