Besides the obvious build failures on heavily sandboxed build servers with no access to the internet, this forces anyone with even a little concern for security to do a full audit of any build recipes before using them, as merely studying and making available the dependencies listed in READMEs and build manifests like requirements.txt, package.json etc., is no longer enough.
I find this a very worrying development, especially given the rise in critical computer infrastructure failures and supply chain attacks we've seen lately.