This is just a misunderstanding of contract law. "Consideration" doesn't in any way mean that you have to receive anything at all. It's basically just a mutual exchange of promises. If I promise to paint your house as thanks for something you've already done for me, and I renege, that's not an enforceable contract because you didn't agree to do anything in exchange. Tokyo promised to put on a race, subject to certain conditions, and it spent money planning that race. There's no lack of consideration in the contract. There might be a breach of a valid contract, but that's a different issue entirely.
I'm not sure what you mean here by "entirely voluntary." There could be a hurricane and it would still be theoretically possible to run a race, but the organizers made a decision about what they thought was safe in response to an outside, natural phenomena that was entirely beyond their control. The Chicago Marathon course closed down due to heat in 2007, and nobody got a refund, even though it was a "voluntary decision" and the vast majority of runners still on the course wanted to continue. The Boston Marathon closed down after the bombing in 2013, and those runners who hadn't finished had to pay for their entries next year, even though it could theoretically have been rerouted. Any decision is "voluntary" to some degree. It's not as though this was a decision made in bad faith, as a pretext to keep the money. This is obviously not something a major marathon has an incentive to do, and the savings are going to be pretty minimal. A lot of the money has been spent, and a lot of what's left will still have to be spent to host the elite race.
That's not how it works in practice. Corporations are terrified of getting hit with class actions for even the silliest stuff, nevermind situations where consumers have actually been harmed. And while in the U.S., consumer arbitration has largely replaced class actions, consumer arbitration is extraordinarily easy, cheap, and favorable to the consumer. That doesn't mean most people do it, but usually you can do it over email and the phone, and the consumer usually wins. And that's not even accounting for the overwhelming majority of cases where the consumer demands arbitration and the corporation just caves; corporations usually only go to consumer arbitration if their lawyers think that they're being taken advantage of.
Credit card chargebacks are decided by low level employees on an ad hoc basis. You very well may get your money back, but it doesn't mean you were legally entitled to. A lot of it just comes down to what's easiest. If the consumer is complaining about a small retailer or entity, the credit card company knows it can effectively do whatever it wants. If it's a larger entity, the credit card company will look more carefully at the basis of your chargeback request, and will deny it if your right isn't clear. Basically, credit card companies do not want to be in the business of arbitrating contract disputes where both sides have reasonable arguments.
Anyway, if you request a chargeback knowing that your contract said you're not entitled to a refund, then you're committing fraud. You might get your money back, but you're a dishonest person. Be a grownup; honor your agreements.