[tallytarik]

Much of the internet still does not support IPv6, so most providers will give you an IPv4 address. In fact only a few providers even support IPv6 at all.

Even with IPv6 it's not a huge problem. With a few samples we can know that a provider is operating in a given /64 or /48 or even /32 space, and can assign a confidence level that the range is used for VPNs.