[jgrahamc]

I think because Lee Holloway (the technical founder of Cloudflare) was used to use NGINX and so he used it for the original architecture. It's also the case that Pingora replaced part of something that handled both connections to origin servers and reading from cache. So the comment about "not serving files" isn't 100% correct as the NGINX instance was serving files as part of its work.

[xani_]

Well, it does offer more varied stuff from the get go so I can see why someone wouldn't want to limit their options, HAProxy was and is purely a proxy while NGINX is a bit of everything.

SPOE/SPOA added a bit of programmability to HAProxy but it is still basically only messing around with headers and acting upon that, nothing to do with content.