Holy days of obligation are a complicated issue, at least in the United States.
Except for Christmas, religious holidays are not also secular holidays. That means that if there is an obligation to attend Mass it must be added to a day that already has obligations for work, school, and all the normal daily/weekly activities in a family’s life.
Relatively few Catholics actually attend Mass on holy days. Compare the schedule on a Sunday (when there may be five or six Masses available) to the schedule on a holy day (when there may be two or three Masses available). If people were attending on holy days at the same rate they attend on Sundays those two or three Masses would be overflowing. But in my experience, the churches are half empty.
And then you have the holy days that are sometimes days of obligation and sometimes not. Several of them have the obligation abrogated when the holy day falls on a Saturday or Monday except Immaculate Conception and Christmas. And then you have the Ascension which is observed in the northeast and Nebraska, but not in other parts of the country.
There was a time when I thought we should observe holy days more often – move the Ascension back to Thursday and eliminate the Saturday/Monday rule. But I’m beginning to think that all this does is make it harder for people and moves them away from the Church and that’s not the direction we should be going. Perhaps it would be better to make holy days optional days for Mass and also add in opportunities for other observances – what about a Mass for workers on Labor Day, a Mass for wisdom at the beginning of the school year, a Mass for the parish’s patron saint, and other local observances.