Protestant here.
I'm going to guess it's because:
A) They don't want to start a debate.
B) They rather ignore having to deal with the epic Bible pawnage which might lead to doubt threatening their entire world view.
Ignorance is bliss?
"Ignorance is bliss?".
That same phrase can just as easily be applied to one who would rather deny the existence of God and the possibility of there being an ultimate spiritual truth to submit to. To a person who doesn't like the idea of not being able to do whatever they want whenever they want, they are merely worshiping their own body and intellect, rather than God. Everyone is a worshiper, the only variable is what you choose to worship. Money, success, sex, food, fame, comfort, respect...you can add almost anything to that list, but they are all just functional saviors that one might put in place of Jesus.
To be fair, there certainly are Christians out there who have never spent serious time contrasting their beliefs against the "light" of science, and thus are ignorant to what scientific arguments might entail. However, to assume that because of this, they are somehow less in touch with reality, is a massively audacious conclusion to arrive at.
I have absolutely no problem speaking up and talking about the Bible here, but I am so outnumbered on these boards, that for every one point that I might articulate (especially in regards to the God vs. science debate), there will be ten people who will bring up something different, and I will never be able to keep up. Not that I don't want to answer legitimate questions and make my case, but practically speaking, it will eat up hours and hours of my time, and it's not like any of you are seeking to learn from me anyway! It's just not worth it for me to get involved in this kind of context. I know what's coming... "OOOH, OUR ETERNAL SOULS ARE NOT WORTH YOUR TIME? GOTCHA." The truth is that God is the only one changes someone's heart and nature, not other people. That doesn't mean Christians don't ever have to try to talk to anyone about spiritual things, but it does mean that my engagements with people should be Spirit-led (as in Holy Spirit), rather than just me deciding on my own that it might be fruitful to pick a fight with a bunch of athiests who already have spiritually hardened hearts.
You science guys definitely amaze me though, in that you are so absolutely certain and convinced that science has all the answers, and that there is no room for a spiritual realm to exist. As I've stated before on here and got no response- if God exists, then he is the author of science, so how can his existence be threatened by science? The only answer to this question is that you are unwilling to consider worshiping something other than your own fleeting desires.