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They don't have to collude, the third party advertisers that collate and provide shadow profiles do that work for them.

• vkou 10mo ago
  The advertisers don't get the raw data feeds necessary to do that.
  • ehnto 10mo ago
    What raw data do you mean? They get so much data, it's hard for me to imagine anything that might be missing relevant to this context to be honest.
    • vkou 10mo ago
      Do you work on ad platforms? If you did, that imagination would be reined in quite a bit. The gist of it is that the platforms carefully curate what data they provide to their customers. They don't want to give anything low level away, both for compliance reasons and because it would undermine their own business. Facebook makes money by charging for access to their users, not by giving away enough information about them for one of their customers to become a competitor. Almost all of the data the platforms provide is 'How well is your marketing campaign doing and among whom' - on a high level. There are issues with poor designs leaking information when the campaign only hit 20 people, but as a general rule of thumb, but that's an exception, not the rule.
• Teever 10mo ago
  That's the collusion that the OP is talking about. It's just done through middlemen.