I think the reason the US cares less about Afghanistan than they once did is obvious. The frequency of fatal violence against American troops in Afghanistan has fallen so drastically from the old days that most Americans without active servicepeople in the family don't regularly remember the mission is ongoing. If we were still losing 200-400 people a year over there, it'd be a far more proximate issue for most. And THAT'S a factor of us only having ~5,000 people over there rather than ~25,000 people over there like we did back then, too.
We need to get out of these countries