why didn't they just get a pmc to take over and let everyone get paid? 
That was Flynn's idea. They were going to privatize the war and pay Erik Price to fight it (or rather have the Afghans pay for it)
The Trump - Taliban deal was drafted in a way that if the Taliban would stick to it and join the Afghan government,
they would eventually be 'forced' as part of that government to sign a security agreement to keep the contractors and help US special forces fight terror.
Today Milley admitted that the Taliban did not act in accordance with the Doha agreement and that the alternative to pulling out would be a renewed conflict with the Taliban or rather full scale war.
The only thing the Taliban did out of the conditions outlined in the agreement was not attack American troops. They calculated correctly that the US would leave and not risk more lives.
