People like making up reasons and presenting it as fact on the internet lol, but actually working in a school, here are the real main reasons. Busses are compartmentalized and busses have padding everywhere on the seats and they’re densely packed so it’s usually safe enough without belts if kids get flung around. They also typically drive slower than cars and no seatbelts make evacuations easier and faster for students. They are also very heavy. I’ve been in a bus that’s been hit before and it was like someone just slightly shook the bus while the car’s headlight was busted. The paperwork being done took longer than taking us home. The last reason is probably the most believable, but it’s to cut costs, too. Busses with belts can range $8-15k more expensive and school faculty members are underpaid enough already.