Hundreds of Baloch nationalist terrorists have refuge & protection in (& arms from) Afghanistan over the years, definitely from Karzai (as seen by Wikileaks) & probably through US support as well. The recent resolution on Balochistan in the House of Representatives was equally outrageous. It is also opposed to the Iran-Pakistan pipeline project, that too passing through Balochistan, Pakistan. And to top it all off, the US has recruited mercenaries in the garb of diplomats in Pakistani consulates & embassies, as indicated by the Raymond Davis affair (& there are other examples as well).
With the US stirring the hornet's nest in Balochistan, the Pakistan government will be out of its mind to let the US have a consulate in Balochistan, unless it is truly 'bought' by the US.