You may not like it, but just because the location is closed, for whatever reason, they are still paying bills for overhead costs and taxes and employee things. Things that don't stop just because the building is closed for those days.
As many said, alot of preschools and centers calculate the yearly cost and divide out for monthly or bi-monthly rates. I do home childcare and for me, I get paid holidays but my vacation and illness days are unpaid.If parents are ill or they go on vacation, I still get paid, just as you likely do at your program. They plan for you to be there and to get paid for it. They still have to pay the electric bill and the rent and such.
Most child centers, daycares or preschools or even classes, you pay based on enrollment, not attendance. You sign up and pay for that spot to be reserved for you..not just for the days you are there in the building. That is the agreement you make. Again, sucky for you since you signed on at the end of what is their "year" and will have to re-up with supplies and such soon (weird too for a school-situation..most go Sept-June, with a summer session as well).