We're just too comfortable. Too comfortable in our habits and our celebrations. Too comfortable in the kinds of parties we throw and the language we use. Too comfortable in our friendships and our relationships. This is why that statistic is what it is. Christians in the US have the unique blessing of living in a country that has not only the legal and social framework needed to breakdown the ugly, separatist nature of humanity, but also immigration patterns that create environments ripe for interaction...but most of us stay comfortable. We squander the opportunity for people to see what the life of a person working out their faith looks like up close, on a day to day, human level.
I read quite a bit of Seth Godin and he talks about the "lizard brain" a lot. It's that part of your brain that wants food, shelter, that second slice of pizza when you're on a diet. It's the one that keeps you from starting an exercise program, speaking in public or taking a leap into an uncomfortable new project. That's...all that's going on here.