Web-based tracking is done via browser fingerprinting and cookies. IP addresses aren't reliable due to NAT and organizational proxies.
Also, I'm not sure what your experience has been but my IP only changes very rarely. Seems to happen about once every 6 months. My understanding that this was somewhat common, at least in the land of cable/coax-ISPs. Is 6 months not long enough to glean anything useful?
But proxies will still group the users on the same IP.
Which is why I personally surf with cookies disabled/blocked by default. So with dynamic IPv4/IPv6, that leaves only browser fingerprinting.