Most do? There are higher concentrations of textbooks in some places like the library or bookstore, which do provide textbooks to students, but there will also be a ton of them spread throughout various offices and some classrooms. It's no surprise to me that they could fill multiple dumpsters with just textbooks.

Though hopefully they don't just trash all the furniture, as there could be millions worth of desks, chairs, tables, and shelving units, depending on how big the school is.