Because in the US, taxes on vehicle imports are practically nothing, its basically only the transportation and handling fees when cars are imported from Germany, Italy, UK, Japan and the like. That cost is barely $1000 at max.
Also, a lot of these cars are built in the US- many or most BMWs, Audis, Toyotas, Hondas, Hyundais are built in the US with almost no taxes, government fees. So the customer just pays
cost of producing the car) + (company profit) + (dealer profit)
which amounts to about half the cost in PK. In Pakistan, there is a tax on importing vehicles; as much as over 100%. So if a brand new Benz costs $50k in the UK or Japan, you gotta pay the $50k to the car company + $50k to the Pak govt. and possibly even more. So you end up paying $120k or so for a $50k valued car.