Google is literally the market leader at using personal information to make money. In any sensible business plan, they'd be the ones buying data, except they don't have to, because they're also the best at collecting it!
In general people greatly overestimate the potential gains from selling data relative to collecting your own. Most personal data is fairly general and bland and useless. Gains come from very specific data that caters to your particular use-case. The best way to get that data is usually to collect it yourself, not just because it's so specific, but also because tiny details in collection methods matter, and the only way to make sure it's been done right is to do it yourself.
In general people greatly overestimate the potential gains from selling data relative to collecting your own. Most personal data is fairly general and bland and useless. Gains come from very specific data that caters to your particular use-case. The best way to get that data is usually to collect it yourself, not just because it's so specific, but also because tiny details in collection methods matter, and the only way to make sure it's been done right is to do it yourself.