How would they be tied together in the first place?

Also if you consider the implications. "Just take a new identity online every 2 months" sounds easy to say, registering an HN account is certainly not a big deal, but it implies that you must also delete cookies from all browsers (desktop, laptop, phone), delete data from all apps that use the Internet and you want to change your identity on, reset your TV if you make use of things like netflix there (because if it has internet, then it probably also tracks while watching regular tv). While doing this, the devices must remain offline, then you change your IP address, then you can use them again. Else, an app will ping the mothership before your IP changed and get a cookie that it will use again after the IP change, binding the IPs together and leaving a trail of your historic IP addresses on some server.

It's a lot easier if you share an IP with a hundred other people, such as with a VPN or CGNAT or many schools/businesses. Then you can just reset the cookies you want without it being able to fall back to another unique identifier.

This isn't even considering device fingerprints such as created using html5 canvas or audio APIs.

I don't do this myself, I'm just saying there's a lot more to it than picking a new HN name.