> A 404 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls

— https://datatracker.ietf.org/doc/html/rfc7231#section-6.5.4

This why in a lot of contexts it would be good to at least be micro catching them. If they were cached for 5 seconds it would have covered all subsequent requests.

404s have got to be very cheap to serve

Not when you're on a metered connection, or on a high latency one.

Don't make your customers pay for your sloppy habits is a good policy to have.

If the CDN returns a 404 or the origin server, then your satellite phone is still waiting.

But they aren't always!