It’s pretty simple. A VPN adds a layer of privacy between you and the server you’re accessing. You go from user A with X home IP address originating from precise Y location, to user A with generic shared IP originating from a vague location likely nowhere near your real location.
Beyond location, did you know there are services that can sometimes accurately provide a users place of work based on home IP? Their likely income level, and more. That becomes impossible with a VPN.
In short a VPN removes a key personal identifier that can be used to ID you online. Your IP address.
But traditional ISPs reuse IP addresses too. You rarely get a static IP from your ISP. Some even run carrier grade NAT and you're literally sharing an IP with your whole building or something. VPNs are not really different in any regard. They do obfuscate location, I'll give you that, and that's seems like the crux of the issue with traditional ISPs: they are small and distributed so people have created location maps. By using a big centralized service you can obfuscate your zip code. I'm all for people having that option, don't get me wrong. Personally I'd rather see us pass strong legislation that takes things a step further and prohibits zip-code based profiling if that's considered dangerous to society, or ya know solve the social problem and create diverse zip codes in the first place so you can't predict income based on it, rather than be fooled into thinking that we can solve this problem by giving everyone a VPN. It doesn't scale.
Most residential ISPs reassign the same IP to the same account for months at a time. It's not technically static but is certainly used as a "mostly static" piece of data by profiling technologies.
Beyond location, did you know there are services that can sometimes accurately provide a users place of work based on home IP? Their likely income level, and more. That becomes impossible with a VPN.
In short a VPN removes a key personal identifier that can be used to ID you online. Your IP address.