I don't see how this is complicated. US has a lot of allies and those allies have agreed to this. Turkey does not have a lot of allies (or at least as strong of allies as the US has/had) and thus doesn't have the same agreements in place.
I mean look at the international outrage when people from country A commit a crime INSIDE country B and country B punishes based on their own laws. The north Korea prisoner who was tortured and died shortly after release stands out, but there are plenty of other examples.
To just say "I don't see how anyone has a problem with this" makes you sound like a shill or someone trying to look enlightened, because it's not hard at all to see how this is complicated.
I'm hoping that he is extradited and stands trial because I can't think of an alternative. It will settle the issue as best as we humans can.