It could be just "good enough" as it is. That is, as another poster commented, there is a Th1 or a Th2 reaction. And these in a sense compete. Only one appears to be active.

The current framework of our immune system could go back quite some time. Even to our mammalian cold-blooded ancestors, 200? mya. When I think of cold blooded, I think of creatures able to remain static and at rest for a long time, periods of low-energy usage. So maybe this framework comes from before warm blooded mammals?

And, if it works well enough that people can breed (which used to be 15 years to 30 years old), and if dying after, oh well. Why evolve better? Or maybe too much monkeying has downsides.

Look at sickle cell anemia. Quite beneficial with malaria parasites around, not so much without them.