She *said* it was because she missed her family. However, she started "missing her family" immediately after she got the message from her sister that Anthony was getting a divorce.

According to the monthly letters, he had everything but the last chapter (which he'd just finished) backed up and in copies in various places. So it was for the sake of the last chapter. Still an asshat thing to do, given that (in a real life equivalent situation) one would not only be putting one's self and family at risk, but also the poor firefighters who then have to go in after the idiot.