But it doesn’t.
When you move track segment you can place it over edge cut line exactly as you can place footprint there.
I frequently place footprints in several groups out of PCB and make there local connections and then move the whole group inside PCB.
How do you suggest KiCad should behave:
it should not allow to move group over edge cut line (I would have to left opened ‘gate’ in edge cut shape to have a way to move block inside PCB),
it should allow for move block over edge cut, but when it happens that you stop moving just on the edge cut your group will be damaged by deleting all tracks colliding with edge cut and shifting out or in footprints colliding with edge cut.
KiCad allows you to have many not acceptable for final design situations during work. It would be very hard (or even impossible) to use it if you will be not allowed for it. At the end you run DRC to check if you managed to remove all such states.