The beauty of electronic displays is that they can be tailored to your specific wants and needs. If I want to view your text, I should be able to view it at a size that's comfortable to me on whatever device I want to read it on. If I'm not reading it, and am instead waiting for updates, I should be able to scale it down and put it somewhere in my workspace that doesn't take up too much room or distract me.
To have an edict that says 12pt must always be 0.4233cm or 0.16777in (quite a ridiculous measurement) achieves nothing. What if I want to display the resource you built for display at 12pt on a 24 inch monitor? A 6 inch phone? A projector? What if I have bad vision and want it larger? Suddenly, 12pt needs to get multiplied by some arbitrary factor and it's lost all of its usefulness again.
My expedient excuse is that it's not necessary unless you're dealing with something static and physical.