The reform was instigated by the Catholic Church. Catholic countries most adopted in immediately. Britain not until 1750. Russia not until 1917. Orthodox Churches still use the old calendar and have Christmas 2 weeks later.
The Orthodox Church is all wrong. The Gregorian calendar guarantees that March 21 will always be the beginning of Spring, etc.
Anyone who favors the Julian calendar is out of touch with the reality of the seasons.
Thanks!