"Churchgoers" is a vague title. But the population being surveyed isn't anywhere close to that population.
Among many "fundamentalist" or "ecumenical" church attendees, most of them past the age of 25 have probably been "forced" do read it through their bible study groups within their churches. When you get to your more common "protestant" congregations, as well as members of the RCC, it's very likely they've only read what was assigned in some theology based education that they had and often that will be well short of the whole book. Furthermore, they aren't all working from the same "bible". There is an RCC version and a more common "protestant" version. Heck, even the 10 commandments aren't the same between all versions (they number them differently).
Within my own experience, and one of my frustrations with organized religion, was that most "church goers" don't even really have "faith" in any strict sense. They were attending for the sense of community and for the access to moral education for their children. Their "faith" was highly elastic. None the less, those very few with any true sense of faith and adherence to it, were interesting people to know and engage.
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