Early in the history of computers in schools, they typically purchased and supported only one operating system. Schools were “Apple” schools or “IBM” schools; later they were Macintosh or Windows schools. Ostensibly, decisions were made for financial reasons (PC’s were generally assumed to be less expensive than Macintoshes) or for educational reasons (“PC’s are what students will use in the reals world” or “Macintoshes are easier to use”). The reality is that many schools adopted the platform preferred by the first IT professionals hired by the school.
A colleague worked in a school system where the first computers were Apples, then Macintoshes. A tech-savvy teacher (who moonlighted as a computer salesman in a business selling Apple products) installed and managed the computers and servers. He became disgruntled and refused to turn over the administrator passwords for the devices he had installed. The school hired its first CIO and that individual was directed to never purchase Macintosh computers. That was decades (and multiple CIOs) ago, but the school district still does not allow the purchase of Macintosh computers.