Adding up weak arguments does not make a strong one. Zero plus zero is still zero, so a pile of failed proofs proves nothing.

That would hold if each argument had zero force, but that is the thing in dispute. If each raises the probability even a little, they combine, the way several independent clues raise the probability of a verdict. The atheist has to show each argument has no force at all, not merely that none is decisive alone. Swinburne makes this precise with probability. The reply zero plus zero assumes the conclusion.