A lot of the bizzarro WT theologies and wacko, loonie-tunes doctrines are stemmed to how the Judge Boozerford formed opinions on things and the Borg continues to go with them today.
The Borg realizes that it would take too much effort to change it now or is too cheap to do so. Probably because having the sheeple observe holidays it would take away from the focus on the Borg and the Borg knows this. Harmless things like birthdays, mothers and fathers day.