I have a couple hunches. For one, I think these folk have bought heavily into a crude narrative of how our civilisation has made the scientific progress that is has. This story paints philosophy with negative moral tones and orients its adherents' very sense of what is noble and courageous away from it. The story is more familiar in its anti-religious form which goes something this like; “before, we, in our hubris, used to explain the world superstitiously by appealing to spirits, ghosts and all sorts of things that had anthropocentric concerns, but now we know that the world does not revolve around us and that we need to humble ourselves by carefully studying nature, letting our observations of her inform our ways.” This story can get broadened to encompass philosophy too; “before, we, in our hubris, used to think that we could figure things out by sitting in our chairs and just thinking, but now we know that we need to actually get out into the world, observe it, and let nature teach us how things are.” Philosophy, then, gets branded as prideful (for it assumes that the world is so much like us that by using our ordinary, intuitive concepts we can simply think our way to answers), and lazy (it is unwilling to step out into the world and wrestle with it). Science, on the other hand, is contrite and courageous. The scientist has learnt, perhaps the hard way, that the world is strange and cannot be properly explained using “common sense”. She is thus humbled and thirsty to learn. She is brave too, willing to get messy through actually exploring and observing nature. Her humility carries over also into her openness to correction. Nature can show her theories wrong and the scientist must bow before the data.
For a person persuaded of this narrative, their entire sense of where we've come from (who we are, therefore), and even themselves individually as a part of this, is pitched with philosophy valenced as undignified and unworthy. Science is exalted as a higher way of being and the two are at odds; philosophy was part of the problem holding science back. It is interesting how the new atheists display such reverence for science (beyond, I think, typical respect for its achievements). It is possible, in having this sense of things, to feel deep admiration for science and awe at the world it's revealed and the technological feats it's delivered, while painting philosophy as stagnant, sad, old-world and crusty - archaic and even threatening when it continues to assert its relevance. The integrity and progress of science thus requires, according to the new atheists, the retreat of philosophy.
Secondly, it seems to me that the new atheists think that their position is blatantly, obviously true. Consider a contrast case. You can be an atheist but think that, actually, the question of whether God exists or not is a profoundly difficult one. You may have reached the conclusion of atheism, but it took you a lot of hard work and thought, and you can see how, somewhere down this difficult path, someone could veer off and go in a theistic direction. In other words, you think it's conceivable that other, equally intelligent and rational people can, without forfeiting that rationality and intelligence, disagree with you on God's existence. You may think they're wrong, “but hey”, you think, “this is an important and difficult question where intelligent people disagree.”
Well Dawkins are co and not that kind of atheist. To believe in God, in their eyes, just is to step into irrationality and delusion (watch Dawkins' current show on Sex, Death and the Meaning of Life, and see how often a “religious” view is contrasted with what he calls “the rational” view). But this sort of exasperation-come-disparagement flows most naturally when you are convinced of the plain-as-day, transparent, obviousness of your beliefs. If somebody, say, doubted that the sky is typically blue, you could only reason with them so much without them agreeing, before you start to write them off as irrational. That the sky is typically blue is just obviously true for anyone able to see it. To fail to believe it is to have something seriously wrong with you cognitively. From the language of the new atheists, it's clear that they feel similarly about the non-existence of God. God's non-existence is seen as so obvious (to a modern, scientifically educated person anyway), that to not accept it is to show that you're intellectually impaired.
It's no wonder, then, that these guys have a hard time with philosophers. With Socrates as the paradigm example, through history philosophers have been annoying people by pointing out that life is a lot more bloomin' difficult to figure out than you might think. Although I reject the view that “there are no answers in philosophy, only questions” philosophy does show you that reaching those answers can be hard, difficult work. A philosopher will slow you down and show you that, even if you're ultimately right, there's a lot more nuance and subtlety you have to consider before you can really say that you've successfully made your case. This is something you will have absolutely no appreciation for - indeed mostly frustration and incredulity with - if you think that your views are already blindingly obvious. You'll want to see people believe them and take action on them, not debate some (to you) irrelevant, besides-the-point, minor detail. You'll fear that people will miss or avoid the obvious bigger picture and you'll get angry when they appear to be doing so. If your views are clearly correct then it's just obfuscating, obscurantist sophistry to try and undermine them with some clever-sounding logic-chopping. Dawkins wants to steam-roll ahead with his cause, not be told that the central argument of his book confuses two senses of the word “simplicity”. Here, then, is another source of new atheist contempt for philosophy.
1Richard Dawkins is actually directing this insult at philosopher Anthony Kenny but it's clear that he's using the fact that Kenny is a philosopher as the insult itself. At any rate, the full post is available here. Peter Atkins' comment comes from his debate last year with William Lane Craig in the Q&A (full debate here). Laurence Krauss gave that comment in an interview here.