There are lots of ways to approach meaning, and more broadly spirituality and community, without theism.
This is a weird take on atheism that reads like you've only seen atheists online creeping out of /r/atheism or some similar place. There's no more reason that "why" should be answered by Christianity than by any number of philosophies that don't require a god, and pegging someone as arrogant for ascribing to those beliefs is silly.