Yeah but I am afraid every other website on the Internet is not done with the care and good craftsmanship that the gov.uk applies to its website. I wish, though! But then so many web devs (and so many of their managers, too!) would be lost without knowing what to do without a JS framework that weights several MBs worth of bloat...
It's about cost. If it takes a web dev a day to progressively enhance a page from html through css and JS, then it's a day they're adding value to a small slice of the users.
Even if you multiplied the 0.2 by 10 or 20, you're still looking at a slice not large enough to build for.
I'd say it's about priorities (i.e. very much related to cost, but with slight differences). That's why I mentioned the lack of people who cares. If you as a manager care, or if a dev with enough decision power cares, it will just be included as part of the time it costs to get the website done.
A worker putting a helmet and appropriate clothes is losing time that could be beter spent producing value. Or if we talk about social policies and minorities, for example, even if as the word says, it's a "minority" of people so it might seem that it's a slice not large enough to improve for. A bit extreme examples, but you get the idea.
Also a 0.2% of all world population is still a huge amount of people. It's just that people who can take decisions, just don't care. But some people do care, like those in charge of co.uk websites, and then we all see how well things can be done and how poorly we've been doing in comparison.
