An encrypted 'digital locker' is a naive and unreal solution, at least until homomorphic encryption is mature. How would I request data I'm interested in from people without knowing if they have it in the first place? Issue a million requests? And if I'm issuing such requests, do people have to pay me now because it's data that I have generated?
We are agreeing on the terms and policies of all information services we use and generate data from. It's not like they took us by surprise, except for few Analytica cases of course. If we follow the data ownership argument, which has (re)surfaced mostly due to media attention on FB and the likes, such services will become dysfunctional right away.
Privacy isn't the weak argument, it's just not very well enforced yet mostly because most people don't care much. Ideally, if a company wants to sell your data, as part of their ToS/PP, they notify you. If you approve, you get a share of that sale (basically what Nukleosome is doing). If you don't, they just move on.