> Externalities lead to users downloading extra gigabytes of data (wasted time) and waiting for software, all of which is waste that the developer isn't responsible for and doesn't care about.

This is perfectly sensible behavior when the developers are working for free, or when the developers are working on a project that earns their employer no revenue. This is the case for several of the projects at issue here: Nix, Homebrew, Cargo. It makes perfect sense to waste the user's time, as the user pays with nothing else, or to waste Github's bandwidth, since it's willing to give bandwidth away for free.

Where users pay for software with money, they may be more picky and not purchase software that indiscriminately wastes their time.