I didn't put binary support into pip because (a) it didn't work well on some systems, and (b) I didn't use the other systems. I am not aware of rejected patches to support binary packages on Windows (where it would be nice to include), or even rejected patches on other systems (where I think it would be misguided).

That this functionality still doesn't exist years later I think is due in part to the problem domain – people find it easier to change parts of their workflow than to add this functionality, and the whole problemspace is kind of hairy which makes it hard to advance without causing regressions in somebody else's weird workflow. (And admittedly the code is hairy too – but who wants to fix that? I don't! No one does!)