I understand the concept perfectly and that works where the currency is money (because we (mostly) all understand the value of money).
The problem arrises when the currency is personal data. How many people have even *thought* about how much their personal data is worth let alone begun to put a monetary value on it? Very few in comparison to how many people know the value of money. And it’s this ignorance that companies like Google and Facebook rely on.
Luckily the tide is slowly starting to turn and people are starting to begin to be aware of the fact that their personal data has value. And as people become more and more aware of that, questions will be asked as to how much they should be receiving in return for that data, and how people can take control so that they can choose what to sell.
This will likely all require government intervention as the companies raking in the profits from consumer ignorance aren’t going to voluntarily give users these controls.
How do you propose we make money from our data? Who do I sell it to, and how?
Plus, surely the trade off with Facebook/WhatsApp/Google/etc being free is that we are giving them our data for their 'free' service. Rather than pay for it? Yes Google could pay me £10 a month for their service, but then charge me a subscription fee of £120 a year. What's the difference?