Providers track DNS requests
DNS requests are almost always unencrypted, and it benefits the ISP’s to keep them that way. They aggregate all the searches to provide intelligence for marketing. The problem is that our weaponized law enforcement can request that data without our consent. Then they can target American citizens with more invasive collection of data passing through the ISP.
Providers can identify PC making the requests.
I am pretty certain that the device being used on the Internet can be identified even though it resides behind the ISP gateway. It never occurred to me that the MAC address of the device was visible to the code running in the browser. On cell phones the MAC address is random, but the phone is pretty easy to identify with the traffic to the cell phone provider. With IPV6 the devices inside the ISP gateway can be visible directly, which is awesome for gaming. Not so much for security. AT&T has chosen to protect their users of IPV6 by having a 1:1 NAT. The only problem with that is the loss of 15 \64 subnets that ARE available on Comcast IPV6.
Clicked search results are tracked by provider.
Search results have a lot of code behind them. When they are clicked on the search provider records the request and the website is loaded by handing off the DNS request to the device.