The only reason humans can do this is because our language interpreter is separate and parallel to our language parser. Unless we are making a language processing chip (transistors can be fully parallel) we want to avoid wasting work.
Neurons are a bit like transistors, it's a lot harder for them to rewire than for them to perform their already-assigned task. As a result, it is most efficient to have blobs of neurons configure into task regions and do the same thing over and over.
If you've already got a hardwired parser and a hardwired interpreter, there's really no reason to not have them run in parallel. (We have plenty of calories to run all the neurons that we need to, so any small chance of a benefit is worth a try.)
