Actually, it does....If you know how virology works.
A virus is a simple DNA mechanism, which mean without a host, a virus cannot survive. Which mean if a virus want to survive, they have to infect something, or someone.
A virus usually try to infect people with geographical proximity. If a virus is found in Africa, then the natural reservoir would be population in Africa. Which mean the virus would either try to infect local population to survive, or local population will get infected by whatever mean (like eating infected pork, monkey or so on) and get the virus that way. What that mean is local population would have infected a least threaten form (or mild form) of the original virus, and then get antibodies for it, and kills off the virus, however, what virus does in order to survive is to adapt to the surrounding antibodies which is gene specific. So by each mutation, they are going to be more adaptive to the local population in order to survive longer to infect other, because that is their way of reproduction.
Hence you will find local virus usually target local population, like Ebola usually wreck the local African population but white people got infected seldom dies. (I think the ratio, I read somewhere is about 63% of infected African dies, versus 26% of other races)
And Zika did spread to USA or Even Europe, they are not local like you said, that is because you are describing the Zoonotic stage (cross species infection). Once it hit human to human, which zika does, it does not limited on mosquito, but rather human movement between population. Another point you need to notice is that South American also have a huge white or mixed population. They aren't as affected as the American Indian in South America.