I can't see why they didn't have a remote learning plan in place already. They should have already had something for snow days.
Hell back in the 80s we had "snow day work" to do just in case.
Some of it's because there is a substantial portion (typically 20%-30%) of kids who, for whatever reason, don't have access to the internet.
If you want to go live from home think for a minute what that means, the teacher has to have an area in their home set aside for broadcasting, not to mention having the supplies and equipment necessary to conduct a lesson.
Which then leads to deciding the
how of the lesson. Teaching on-line, no matter how you do it (real time discussion, live streaming, making an assignment for later turn-in) is different than being live in school.
Also, if you're going to do textbook stuff, even if it's just "Read Ch. 31 and compete
Think About questions 1 and 3, you're assuming the kid took his book home. And no, on-line texts from the publisher don't work unless the school system has paid for them.
If you mean having emergency plans ready to use for this, that is likely doable if you keep in mind that emergency plans are just general, usually just practice that's designed to keep the kids busy and not new material.