Wouldn't companies just update their terms of service to say "you agree to let us buy and sell your data?" Not allowing that would go up against freedom of contract.
In my state there's limited freedom of contract in, for example, payday loans:
https://www.michigan.gov/ag/0,4534,7-359-81903_20942-171016-...
Companies do not have the freedom to offer a $100 payday loan with a service fee of $16. The state says that 400% APR is usurious; by law it's restricted to $15. There's no doubt that without this law, unscrupulous and predatory companies would try to craft a contract which demanded more than that, and we've decided that our society is better off without that unlimited greed.
When people organize and collectively set limits to their exploitation, in the form of legislation (child labor laws, workplace safety rules, ability to join unions and discuss salary, limits on non-compete and similar clauses, etc.), corporations will try to frame this as illegitimate, infringing on their ideal society where the only law is contract law, and they're the ones writing the contracts.
Because organization and collective action on the basis of democracy is the counterweight to the organization based on capital concentration, the latter tries to cast the former as illegitimate.