......what are these so-called private army is doing in Pakistan
......
They are contractors who get paid by and serving the US government.
The same US government's diplomat (and every other government) hires Pakistani staff and Pak security guards. The same way these guards get paid by the US and serve their employer.
Primitive tribals in the Arab land feel that Xi contractors are 15 feet tall, 200 kg gods who can push the Arabs left and right.
In Pakistan however we have not seen the 15 feet tall, 200 kg Xi-gods pushing Pakistanis around. May be we do not consider them gods. Do you?