There's a nationwide shortage of bus drivers. Many retired during covid for good. It is shitty pay and often part-time hours. It really isn't attractive for many people these days, even for retirees.
(The former came in very handy when doing extra-curriculars - our debate coach could drive us to meets without incurring the cost of an extra adult to drive the bus. Of course, given that debate meets start early and finish late, and we still had to do the drive, in practice it meant that a very sleep-deprived and stressed out person driving somewhat erratically.)
All too true. OTOH, "we are X drivers short of the number that our new schedule says we gotta have!" would have been known well in advance. And, post-COVID, any competent engineering firm would have determined various driver staffing level cut-offs, below which the school district would have to operate on a reduced basis. (Closing all the elementary schools, or all schools in the east half of the district, or whatever.)