Whole reason it's January was some Roman administration thing. They needed to appoint some console or something but that could only be done at start of the year, middle of March then. So they moved beginning of the year to January 1st. Now you think they could just have change the other rule but 🤷🏼‍♂

We waited till 1752 to adopt the new fangled calendar in the Kingdom of Great Britain, as it was then. At the same time we moved the first day of the year from 25th March to 1st January. So, Happy New Year, in three months!

Ps the reason Gregory XIII needed new calendar was because the earth being inconsiderate and not rotating exactly to a whole number of days. The Nicene council had long ago fixed Easter to a date determined by the vernal equinox. But without leap years etc that was moving out of position. Hence the "We need to reset here" and the add a day every 4 years unless the year is divisible by 100 unless that is also divisible by 400. Hence why 2000 was a leap year, 3000 will not be.