Outdated transport

Here's something I still don't get. Why do schoolbusses in the US remain unchanged since the sixties when are so many better, more updated and comfortable bus models available?

Every morning when I drop Kevin off at his day-care school, I see the old, yellow, squeeky schoolbusses drive kids to school. Honestly, If you'd judge the country by the schoolbusses, you wouldn't think you're in the number 1 internet/tech country in the world. I realize the look of the busses is somewhat iconic, but they could easily preserve a similar style on a modern bus.

I just don't get it.