Nothing prevents them, people just don't like change. When I was in school (read in grandpa's accent), it was teaching Text602 (https://www.youtube.com/watch?v

Nothing prevents them, people just don't like change. When I was in school (read in grandpa's accent), it was teaching Text602 (https://www.youtube.com/watch?v=2iCUfOPxTp4 https://www.youtube.com/watch?v=2iCUfOPxTp4) and Calc602, which was locally made text processor and spreadsheet tool for DOS. Was it impossible to teach/learn? No. People will just learn what they are thought. There are better/worse options, but that doesn't prevent anyone from teaching anything.