Why can't infectious disease doctors cure mssa?

We can and do: I don't know why you say that. We do it every day. There are many antibiotics active against mssa.The most commonly used are intravenous nafcillin or cefazolin and oral dicloxicillin and cephalexin.Some mssa infections are difficult to cure such as infections of artificial joints, pacemakers, aicd's and prosthetic heart valves. These usually require removal of the device and prolonged antibiotics.