I agree, it seems odd; however, I will state that my kid’s school provides an app that allows you to communicate in both directions with teachers. They also use the app to make general announcements like closure for snow, etc. My wife is generally the one doing non-in-person communicating so I haven’t actually used the app (I only recently learned it exists), but hopefully the teacher can filter notifications outside of school hours.

Were I a teacher, I’d be glad to have a way to communicate without sharing personal information.