So maybe the solution is for governments everywhere demand adherence to the Gregorian calendar and then they all would fall in line? Ducking for cover.
Because making demands of the Holy Orthodox Church proved so successful and not at all destabilizing for such presently thriving regimes as the Roman Empire, Yugoslavia, the Polish-Lithuanian Commonwealth, the Ummayid and Fatimid Caliphates and the Union of Soviet Socialist Republics.
Actually the reason for the use of the Gregorian Calendar by the Church of Finland has as much to do with the Ecumenical Patriarchate and the preference of the local church, the Gregorian Calendar being less of a headache than the fundamentally flawed Revised Julian Calendar of 1920 which by retaining the Julian Paschalion but using Gregorian fixed feast days creates a situation where the number of Sundays After Pentecost and After Theophany but before we start using the Lenten hymnal known as the
Triodion (the start of the Prelenten Period on the Sunday of the Publican and Pharisee, which is approximately Octagesima) balloons, and the period between Pentecost and the first major fixed feast of the summer, the Feast of the Holy Apostles, contracts, resulting in some years having one of the Four Lents of the Orthodox Church, the Apostles’ Fast, having a length in days that is 1 day or fewer - it can be 0 or a negative number, resulting in the fast disappearing, which is unfortunate.
Since the Finnish church receives money from the state, and since it historically celebrated Pascha on the same day as the Lutheran Church of Finland, and since the Finns were accustomed to worshipping according to the rich Sabaite typikon* and due to cold war tensions with the former Union of Soviet Socialist Republics**
which dominated Finland politically with regard to her foreign policy***, it was of some benefit for the two largest Finnish churches to show their solidarity in the face of increased secularism by using a common calendar.
*This is in use in Jerusalem, Russia, Ukraine, Belarus, Poland, Serbia, Georgia, ROCOR, the Metropolia now known as the OCA (both those areas such as Alaska on the Julian calendar and those on the Revised Julian Calendar), and to some extent (at least in terms of Julian Calendar usage in their main cathedral and much of the parishes) the American Carpatho Rusyn Orthodox Diocese (ACROD) set up by the EP in the 1920s to compete with the Metropolia, now the OCA, for Ruthenian Greek Catholic converts, and also on Mount Athos, which uses the traditional Sabaite-Studite Typikon, Athonte vestments of the kind favored in Finland, Russia, Ukraine and other North Slavonic churches with the raised hood (which provides increased warmth and draft protection for presbyters and monks)
** does anyone remember the risque Bravo TV commercial from the late 1990s (before that network got taken over by the most annoying and
effete reality TV shows in the early 2000s, and was instead kind of an art house / independent film network like Sundance TV) which featured a thickly accented film school teacher from “Former Union of Soviet Socialist Republics” where he talked with two contemporary film critics, a Gen-X man and woman who often appeared on that network, and his students, about what made a good name for a movie? It was riotously funny and I can’t find it on YouTube.
*** Hence the term “Finlandization” which was used to refer to situations where the Soviet Union or another Communist superpower came to dominate the foreign policy of an ostensibly sovereign and independent country that usually was not communist in terms of its economy, and in the case of Finland not even formally a dictatorship, although the Center Party dominated elections during the Cold War era to such an extent that one could reasonably refer to Finland as a one-party state; this drama was invisible to most people in the West who seldom paid attention to Finland and would travel there on holidays or just incorrectly assume that Finland was another free, western and neutral Scandinavian country like Sweden, a Switzerland of the North that awkwardly shared a border with the USSR, but people forget that Finland as a Grand Duchy had been traded like a ping pong ball between Sweden and Russia, changing ownership a few times, and during the Winter War, and the Continuation War in the midst of WWII Finland was allied to Hitler and the Axis powers and as a result lost control of Karelia and thus after the war, while de jure independent and de facto capitalist, was also de facto a Soviet satellite state on a leash shorter in some respects than that of Romania, another former Axis state with a huge population compared to most of the other Warsaw Pact countries which liked to occasionally remind Moscow in a painful and slightly embarrassing way that if Nicolae Caecescu were to so elect, he could probably get away with what Hungary and Czechoslovakia were unable to accomplish in Budapest in 1956 or in the Prague Spring of 1968, by reducing Soviet influence, likely forming an alliance with Yugoslavia.
For example, TAROM, the Romanian airline, would purchase several Boeing 707s at the same time it finally took delivery of the rival Ilyushin Il-62M (an equally capable aircraft but one which demonstrated by its delivery date that Soviet technology took a dozen years on average to catch up to that of the West) and began long distance flights to the rest of the world.
Finland on the other hand had to do what Moscow demanded of it, but Moscow let it buy the commercial airliners it wanted, and the Finnish Air Force if memory serves had both Western and Communist types in service, like the air forces of some regional non-aligned powers in Africa, the Middle East and Asia.