They were there. Maybe not in your school district (just like today there are many districts that don't have any chomo teachers), but they existed. The two biggest X factor differences between then and now?
1) There is a digital trail (apps where pictures are sent/stored, phones logging GPS information in real time, etc) for pretty much everything now. 40 years ago there might have been rumors about a teacher (male or female) sleeping with a student(s), but good luck proving it unless the kid stepped forward. Now? There's usually going to be some kind of digital trail (pictures/messages sent) and that's how the vast majority of these situations are being exposed (teacher sends the kid an inappropriate picture/message, parent or another kid at the school sees it and steps forward).
2) There's really no longer 'local news' anymore. If you are interested in a topic, pretty much any topic, an algo will pick up on it and start spitting out stories from all across the country/globe that include that subject. It makes it seem like these things are WAY more prevalent than they really are.