Richard Dawkins' The God Delusion is written for a popular audience; it is explicitly not intended as a work of technical philosophy or to respond to the more abstruse versions theological bullshit. It's explicitly addressed to the billions of people who hold a very specific kind of notion about God and who use a particular set of apologetic arguments, arguments they have mostly received second-hand.
I can't read Dawkins' mind, but I suspect that — besides wanting to make some actual money — there are two reasons he chose to write a popular book. First, he wanted to talk to the sort of people who are not at all interested in works of technical philosophy. Second, I suspect that Dawkins realizes that professional philosophers are mostly complete idiots. Even the ones I more or less like — or for whom I at least don't have utter contempt — are genial buffoons.
With an infinitesimal minority of exceptions, professional academic philosophy is completely intellectually bankrupt. It is at best totally, utterly and completely useless, and I think the profession is actually holding back humanity's intellectual progress. It's simply a waste of a thinking person's time to take any philosopher seriously.