Because the Taliban's definition of a "Neutral Country" is as trumped up and screwy as their interpretation of the Quran. By "Neutral Country" the Taliban means "An Islamic country that will not even listen to what the US has to say." They are willing to push for US isolation but are unwilling to allow Islamic isolation.
They're not talking about handing these guys over to a UN-sponsored war-crimes tribunal a la the one in The Hague. They're talking about a trial by an Islamic run country. There's little chance of him getting a fair trial in the US, but there is even less of a chance of a fair trial in Saudi Arabia, Sudan, Jordan, or any other country where a religion is allowed to dictate law above common sensibilities.
There really is no such entity as a neutral country in this regard. Some countries may not be participating for or against the Taliban, but based on what the Taliban seems to say, there are Islamic countries and Infidel countries and nothing in between.