Why are we still in Afghanistan after the death of Bin Laden?

It doesn't make sense to sacrifice more soldiers than the number of people that the taliban could kill if, somehow, they could get into the U.S. and cause a terrorist attack. Suppose we remain in Afghanistan for 10 more years and 5000 U.S. soldiers get killed. Meanwhile we twart a possible terrorist attack at a train station that would have killed, 100 people. It doesn't make sense to sacrifice the soldiers in that case. We should concentrate on profiling the people that come into the country. And besides, who cares what happens to a bunch of extremist backwards Islamic people in a rogue nation. We can't change their culture, beliefs, or system. How can we convince them that our way of life is better. We can't and shouldn't even want to.