It's a silly way to secular-wash a Christian system. If you want a secular calendar, you should have it not oriented around the birth of Christ. Very underrated decision by the dprk to have their calendar based on the founding of the country.
Interestingly, on Taiwan they have the Republic of China calendar (in addition to the Western calendar) which begins from the establishment of the RoC (1912 on the Western calendar).
Do you believe the Church owns the calendar? Or perhaps Christendom/Christians more broadly?
Any larger change would be symbolic and completely impractical, with waves of inconvenience rippling through civilization. But many non-Christians use the calendar now. We don't want to call this the year of our lord because it isn't our lord.