Comment by vivekd

In ordinary contracts that's true, but this case is different because it's more of a continuing contract

It is not a one time performance like washing a car or shoveling a driveway or buying grocheries. It is a continual term contract where each party agrees to continue going. In these cases, it would be legal to have a clause allowing either party to terminate the contract at any time. Certainly daily stormer was free to stop using cloud flare at any time. And similarly, cloudflare is free to terminate the stormer's account at any time provided they refund the cash. So the contract is not really illusory because both parties still have the obligation to perform, they just don't have the obligation to continue performing.