port files refer directly to URLs of external websites, e.g. for Curl: "https://curl.haxx.se/download/curl-7.48.0.tar.bz2". That is very brittle, in that if that site were to go down, suddenly potentially a lot of programmers can't build their code.

That may be an acceptable trade-off for individual programmers, but for a larger organization having the teams ability to work depend on many external sites may be a deal breaker, unless there was some easy way to (locally?) cache things.