It has been a great wonder for me that why US highschools seems to require expensive programmable/graphing calculators especially those made by HP/TI. I assume

It has been a great wonder for me that why US highschools seems to require expensive programmable/graphing calculators especially those made by HP/TI. I assume it was some deal made by these companies with the education departments of the states and administrations. In most other countries, students complete university undergraduate courses, let alone high schools with only needing a cheap non-programmable calculator, while some courses like an undergraduate course in Computer Science wouldn't require any calculator at all.