Because most of the strikes are in the Tribal areas near the border with Afghanistan where the writ of the Pakistani state doesn't really run. The Pakistani military has received some bloody noses when trying to operate in the area. Even Wikipedia is happy to classify the whole thing as a war[0]. Over 6,000 members of the Pakistani security forces have been killed, 20,000 civilians and 35,000 "insurgents".
Pakistan gets significant military aid from the US to help put down an insurgency by groups that would overthrow the state. On a realpolitik level they also get to blame the US when a strike goes wrong whereas if they were dropping their own bombs they would have to put up with the blame. Mistakes always happen in war, I'd suggest however that a drone strike has significantly more time to conduct pre-launch checks than an F16 pilot does.
But the end result of all that is just that it generates even more hostility towards the US and feeds terrorism. The US is creating its own enemies this way. Again.
Cynically speaking, this is win-win for everyone involved. Except for the innocents who are killed.
The US gets to debug and optimize their assassination program "on brown people that noone cares about".
Pakistan and US also get to claim that they are "fighting terrorism". This breeds resentment and new generations of terrorists to be "fought" in the future (divide and conquer 101).
Plus, who knows when and where the droid program might come in handy in the future...
Pakistan gets significant military aid from the US to help put down an insurgency by groups that would overthrow the state. On a realpolitik level they also get to blame the US when a strike goes wrong whereas if they were dropping their own bombs they would have to put up with the blame. Mistakes always happen in war, I'd suggest however that a drone strike has significantly more time to conduct pre-launch checks than an F16 pilot does.
[0] https://en.wikipedia.org/wiki/War_in_North-West_Pakistan