SMHW:
There is a slight difference between knowing what a HDO is and and knowing what days are HDOs.
Add to that the question of whether it’s an HDO
this year. The obligation is abrogated if the holy day falls on a Saturday or Monday (and if it falls on Sunday you don’t really notice it as being different from the regular Sunday obligation) unless it’s one of the December holy days when the obligation holds even on a Saturday or Monday.
So first you have to know it’s a holy day, then you have to know what day of the week it is, then you actually have to remember to go on a day you’re not accustomed to going…and then you’re likely to skip it anyway because of work or family obligations.
Part of me thinks the Church should just remove the obligations. People would still attend on Christmas anyway. The other days that I often see people at Mass carry no obligation: Ash Wednesday, Thanksgiving, and Our Lady of Guadalupe.