If they accept macroevolution they believe God is a liar.
Or alternatively they believe that the Bible isn't as easy to understand as the crystal-clear physical evidence of common descent.
This is a sectarian dispute between certain brands of Christianity, the scientific evidence being absolutely unambiguous.
Very true:
The "Clergy Letter Project". 10,000 clergymen endorse evolution.
Faith and the Human Genome. By the director of the Human Genome Project, a Christian. Excerpt:
I think scientist-believers are the most fortunate. We have the opportunity to explore the natural world at a time in history where mysteries are being revealed almost on a daily basis. We have the opportunity to perceive the unraveling of those mysteries in a special perspective that is an uncovering of God's grandeur. This is a particularly wonderful form of worship.
"the scientific evidence being absolutely unambiguous"
Really? First I've heard that.