Why do some dioceses move holy days, or not even celebrate them at all. Doesn’t everyone do the same thing?
The short answer is no, not everyone does the same thing. Although the Church is universal, there are many local customs and saints that each country, sometimes just a region, will honor. For example, feast days and patronal days may not be major feast days on the Church’s universal calendar, but are celebrated as such in one place. Holy days of obligation are the same way. The US Conference of Catholic Bishops has a certain amount of discretion in choosing days that best reflect the local church’s experience and history. Another reason certain feasts are moved is a practical one. With limited clergy, or a great difficulty for people to get to Mass, the feast day may be transferred to a Sunday. The rationale is that if a significant feast should be part of the Church’s celebration, then better to do so on a Sunday when people and clergy are available, rather than try to fit it on a day when one or both cannot be there.