My understanding is that these places slowly accumulate their own libraries for some semi-automated framework (like svelte for example, though I don’t think this is svelte). This knowledge comes from my working in a media watchdog, and my own analysis of the New York Times’ code so the economist may be different. I also (obviously) don’t have first class access to these things only what we’ve been able to probe using osint tools and analyzing the javascript/html/css.