Because the more antibiotics you take, the less effective they are when you really need them...
i was once bite by a bat health dept started me on the rabies shots within 8 hours of being bit ....3 days later the results came back the bat was rabid!
yup mine were multiable days with shots i believe it was 1st day that was the worse up my side last shot where i was bitten that was in my chest after that i had to go back,if i rember right 5 times but those were just a regular shot in my hip .....