How come? The investment in time, effort and dotmac fees was long made when Apple decided to close iDisk.
I don't recall Apple's ever undertaking to keep iDisk running indefinitely. The fees were a subscription, which bought a year's service.
Things change; it's a fact of life. We have to plan for it. iDisk had numerous deficiencies, of which appalling speed was but one; maybe whatever replaces it will be better.
Try Dropbox, or a paid service. There's no shortage of them, but none is likely to be permanent.
Jeremy