Holy days of obligation in the Roman Catholic Church are set by local bishops’ conferences, while the Vatican does give some general guidance as to the core number of days.
Previously most feasts that had the rank of solemnity were considered a holy day of obligation, requiring all Catholics to attend Mass on that day.
This was the case for the solemnity of the Annunciation on March 25, as the Catholic Encyclopedia affirms.
This feast was always a holy day of obligation in the Universal Church. As such it was abrogated first for France and the French dependencies, 9 April, 1802; and for the United States, by the Third Council of Baltimore, in 1884.
The Annunciation still remains a solemnity, but is no longer a holy day of obligation, unless a local bishops' conference chooses to reinstate it.
The primary reason for the slimmed down number of such days in the Church is because most countries in the world are primarily secular in nature, and no longer recognize the Church's feasts as days of rest.
