There are several reasons to cancel the marathon: 1. The runners have jobs and obligations that aren't likely to wait for another week. 2. The people who have lost their homes and such have a far greater need for the tons of food/water, hotel rooms, generators, and sanitations workers then the racers. 3. It is really, really, really tasteless to have something so pointless going on when we're still finding dead people and folks aren't sure what they're going to do.
Many fly in just for the race, from around the world.....wouldn't be able to afford/schedule next week, one reason
The cancellation is most likely temporary because he can't be sure just yet of "when" it can actually take place.
Usually due to uncertainty of when the event would take place...