It is intentionally not set in 2023 or later because of "canon events". Those are events from the past set in stone that no one from another universe can interfere with because it would create a paradox that ultimately destroys that timeline they changed.
HOWEVER, this is different than someone within that same universe time-traveling and causing changes that create a branch. (ex. Coulson's team in Agents of SHIELD season 7 went to their universes past, but later in the season caused a branch when too many changes occurred.) Since it's not a different universe until the individual of that home-universe causes changes to the home-universe's past.
Basically, if you're from some other completely different universe and you create timeline changes, you've corrupted the balance of the timeline by bringing outside elements/forces into the past and creating changes. This upsets the natural order and it obliterates everything - timeline and universe.
This is also known as an Incursion.