Teachers are home with even fewer options for child care than before. Some kids can't get to their virtual learning locations. District offices are closed, and above all else, many students simply won't be present with snow outside. That's before any consideration of power outages, which have been few with this storm. I'm not arguing that school is impossible, but this is all still new and it's not a trivial decision.
On the other hand, MCPS did elect to keep virtual learning intact, so it's definitely case by case. We'll see how it goes with MCPS and whether it's a disaster of teachers taking personal days to care for kids, and absent students.