I can think of several reasons someone might choose a service like storj over Dropbox:

• the data is under the absolute control of the owner and no one, no hacker or government, can browse it for giggles
• storage using a service where end users can also be participants utilizes storage space that might otherwise go unused and will have a lower marginal cost than a dedicated centralized service
• Because of the nature of the distributed peers, downloads have the potential to be much faster than they might be from a centralized service.
• The end user could increase the level of redundancy to ensure that short of a complete world collapse, the data would persist. No centralized service can make this kind of promise.
• The ultimate cost to the end user will ultimately pay less for a service that is more robust.

I do agree that it will take a few years for this kind of service to become solid as a rock, but I think the journey is worth it.