Yes. Google and Facebook revenues, for example, are almost entirely from advertising and their ad business models hinge on being able to sell their ability to target very precisely.

Every data point gathered builds towards a more comprehensive knowledge they have on you. It hardly matters if you never log in to a third-party site using credentials from Facebook/Google/etc., that's just icing on the icing on the icing for them. They'll know if you logged in regardless, as long as their widgets or services are in place on a site.

While cookies are certainly the most common means of following you around the internet, there's other means of fingerprinting that, while perhaps not as laser precise, certainly provide more data than most people realize.

Why do you think ISPs are so ardently against people's ability to use them as dumb pipes? And why has the smart TV platform landscape grown like gangbusters (spoiler alert: Roku's CEO has outright said why https://www.theverge.com/2018/7/20/17595384/roku-ceo-anthony...)?

edit: clarifying grammar