Why use meta tags when CSS does the job?

Is there some reason for mobile devices to use meta tags to control their display properties when CSS supports physical units, like points and millimetres?

As someone who has been writing CSS for some time, I find that `width=device-width` and `initial-scale` much less intuitive than `height: 15mm` and `font-size: 12pt` and `@media` queries, all of which have been defined for many years.

Instead of supporting these units properly, I find that devices are requiring meta tags to set their viewports to a pixel size, and with `device-width`, often a pixel size that isn't their actual screen size.

How did the world become this way? Did I miss something while I was asleep, and now these fake pixels are length units in the real world? Or maybe everybody is holding out for a real CSS3 standard, and this is an interim solution? Am I wrong for wanting to use these real units in CSS?