Fuji , if for no other reason, if you can minimize the inconvience that any event causes , regardless how small that inconvience is, then do it out of simple courtesy.Marathons are on a Saturday when traffic is light. There are far more people using the road by running on it, than by driving on it. I really can't fathom what the problem is, it seems like a minority of people feel they're entitled to drive anywhere they want with no delays whatsoever even if doing so requires inconveniencing half the city. Selfish, in my opinion.
Marathons are a great use of the roads on Saturday and the inconvenience really is pretty minor, and to a small number of people.
That alone is reason enough.
If it's not possible, then fine, it's not possible, but is it so much to ask to for them to try ?