You are given advice on how to safely cross a four-way intersection by two companies.

One is an insurance company specialised in people being run over by semi trucks at four way intersections.

The other is a contractor that designs, builds and maintains four way intersections for the government and private entities.

Of course, yes, the later could collude with the former to make extra money.

But it's also not their business model. They build intersections, people pay them to make those safe and reliable. People do not pay them to collude with shady insurance companies which try to kill people by semi truck.

People would actively not pay them if they did that.

Same with Cloudflare. If CF sold data to ad networks, a lot of websites would simply jump ship and use one of the other CDNs with free offerings. People pay CF a shitload of money for ensuring the connection is private and safe (notably banks, governments, etc.)