It's an attempt to align with the West. Most Western countries are protestant/catholic and celebrate on the 25th, so if your goal is to westernize not only politically, but culturally, it's a step towards alienating those who cling to The Old Ways lol

The ROC [Russian Orthodox Church] currently claims exclusive jurisdiction over the Eastern Orthodox Christians, irrespective of their ethnic background, who reside in the former member republics of the Soviet Union, excluding Georgia.

From: https://en.wikipedia.org/wiki/Russian_Orthodox_Church

Politics and religion have always been one and the same: the reason there are two creation myths in Genesis (and many other duplicate tales) is because authors from both Israel and Judea wrote them, often with the aim of elevating their interpretation of Yahweh/El and lowering the importance of the other kingdom. We have Protestantism because an English king got pissy.

This is no different. The Russian church claims dominion over Kiev and they are rejecting that, much moreso than they have in previous years. The ROC is acting as one more arm of the Kremlin and trying to use religion to spread influence.

The Greek Orthodox church celebrates Christmas on Dec 25th so it isn't really an orthodox thing fyi

Jan 7th is because the Church uses an outdated Julian calendar. On that calendar, there are a different number of leap days than the modern one, so the Julian Dec 25th is the Gregorian Jan 7th