> Talking about dates before this epoch makes little sense (any date before the Gregorian epoch will not resemble the same stellar / planet constellation as date after the Gregorian epoch).
That is not the only sense in which we care about dates. For example, we might want to talk about which of two events came first, and by how much. Historians have lots of uses for dates before the introduction of the Gregorian calendar.
Historically, calendars came to be from observing the movement of planets and stars. Now:
> we might want to talk about which of two events came first, and by how much
Neither of which makes sense without having a common reference point (start of Gregorian calendar being one such possible reference point). Trivial example: there is exactly one day between 1582-10-04 (Julian c.) and 1582-10-15 (Gregorian c.), i.e., different reference points.
> Historians have lots of uses for dates before the introduction of the Gregorian calendar.
Yes, and I bet they're hyper-aware about the calendar system(s) they're using. The rest of our mortals can just use Gregorian calendar :)
That is not the only sense in which we care about dates. For example, we might want to talk about which of two events came first, and by how much. Historians have lots of uses for dates before the introduction of the Gregorian calendar.