Here are a few -
Lower tuition.
More flexible schedule.
Some kids don't do well in a classroom setting.
More school options for those in a smaller or OOT community.
Why would tuition be lower?
Who wants a flexible schedule at those ages. Kids need structure.
While a minority of kids will find a classroom setting a hindrance. For the vast majority it is a lot more beneficial, with multiple senses immersed in learning, as well as other social benefits. There are many more that would find it hard to succeed with remote learning.
As
@aygart pointed out, Shluchim already have an online school. It's making the best of the conditions, they would definitely prefer classroom setting.