> It is theoretically possible to program in HTML and CSS, but in practice this capability is limited and inconvenient; merely to make it do something is an impressive hack. Such programs ought to be free, but CSS is not a serious problem for users' freedom as of 2019.
Well… https://keithclark.co.uk/labs/css-fps/
You could also argue that DOCs and PDFs are software.
I'm sure he'd agree that people should also not include proprietary software in those files as well, but doing so is far less common than webpages, at least for stuff the average user is going to run into.
And how many people are actually programming in HTML/CSS vs JavaScript? A proof of concept is one thing, but most users won't run into it.