Why did the word "chalkboard" replace "blackboard"? Is it because "blackboard" was deemed offensive or some other reason?

The term 'blackboard' was not offensive, but calling a 'green' board 'black' was weird.

I remember, very well, when 'green' boards began to be used in the classrooms. Green is a better background for white or yellow chalk, so schools started to replace their black boards with green ones. We tried calling them 'greenboards', but it just didn't sound right, and many schools hadn't made the change, so their boards were still black. 'Chalkboards' became the all-encompassing common term.

https://resilienteducator.com/classroom-resources/the-history-of-the-classroom-blackboard/