While I assume that there are plenty of critical websites out there which are built with efficiency and resource consumption control in mind, the few I have worked on were not.

On those sites you’re right: the approach was different, but not necessarily better. Tracking library bloat and marketing-driven design were reduced. But insane “security” constraints (e.g. “you have to stay on outdated revisions of this library” or “containers are not allowed on the backend, only bare metal”, no joke—constraints that led to significant increased security risk) and extremely user-hostile design practices increased, as well as there being an exceedingly long hurry-up-and-wait turnaround time for shipping important fixes/improvements.

Working on a safety/state-critical site isn’t a panacea, in other words.