The cost of creating new computers has got to be pretty high to the environment (I've heard 85% of lifetime carbon emissions from computers are from the manufacturing process), and I strongly suspect that we don't take that into consideration since we greenwash ourselves by forcing China to do our dirty work, chastising them for it, and then patting ourselves on the back for buying "more energy efficient chips".
I'm surprised someone like the Sierra Club, Consumer Reports, a scientific group, a government group, etc. doesn't undertake it. Yes, it's a bunch of work, there would be uncertainty, but it's essential and better than nothing.
There are such things for food:
* Klimato: https://klimato.com/
* The Big Climate Database: http://thebigclimatedatabase.com/
But if the cost of a new machine is the same as a year or two of the old operating the new is probably the way to go.
They aren't; among other things, most environmental harm is externalized. When you buy things that produce climate change or microplastics, the cost of the impact is paid by society generally.
But aren't those made regardless if the people with old computers upgrade to them or not? I guess over time, they'll make less if people buy less, but the ones we'd purchase today has already been made, and might as well replace less energy efficient devices than just being added to the global count.