Another use-case of GitHub is not mentioned: to get publicity, i.e. to gather stars.

If a website uses fancy new browser features and works for 98% of the population, that means that it won’t work for ~150 million people. If a website makes a change and that works for 98% of their visitors, they’re basically kicking out 2% of their audience. Can you imagine a venue refusing entry to former clients 2% of the time just because they’ve “improved their experience”?