Sounds more like a lot of effort went into fabricating excuses to not make that expense, excuses which are directly contradicted by the National Transportation Safety Board:

School buses use a unique technology called compartmentalization—a passive occupant protection system to protect children in crash. School bus seats are made with an energy-absorbing steel inner structure and high, padded seat backs, and are secured to the school bus floor. Students are protected within the seating compartment much like eggs in a carton. Through our crash investigations, we have found that, compartmentalization alone is not enough to prevent all injuries and that for some of the children involved, a seat belt could have lessened their injuries or even saved their lives.

As a result of our school bus crash investigations, we believe—and have recommended—that, when investing in new school buses, the purchased vehicles should provide children with the best protection available, which includes lap/shoulder seat belts.