The focus on the spike protein is due to bizarre fixation on neutralizing antibodies such that the rest of the immune system practically doesn't exist. The "simple" (nothing dealing with the immune system is simple) fact is the immune system has multiple layers of defense and the ability to neutralize a virus with an antibody is just a small part of it. I am completely unsurprised that in our attempt to outsmart millions of years of evolution we ended up doing something completely backwards and wrong.