The OP asked a legitimate question. Especially considering how a particular and significant portion of a Christian segment of US Society indeed does view the GOP as the more Christian Political Party.
I'll just note this though: That Christian segment mostly supports the GOP due to its' views on Moral Issues than on its' Economic Views. However, they have largely adopted and/or shaped their Religious Belief regarding Economics around the GOPs' views in the process. In part their Belief is centered around the Bible and in another part they have centered their Belief around the GOPs' policies.
On the GOPs' side, they are mostly simply interested in getting Votes. They have not claimed that their Economic Policies are Biblical or even their Social Policy which attracts certain Christians for that matter. The GOPs' main incentive is not the Bible, but Votes and it just so happens that Bible Believing Christians were a large unaddressed Voting Block that they could exploit for their own benefit.
So in essence, the GOP doesn't need to explain the Biblical aspect of their Policy. That is for the Christians who espouse the whole of the GOP Policy to explain. That said, not all Christians who Vote GOP agree with the whole Policy of the GOP. In fact, when asked, many are aware of certain conflicts with the Bible and the GOP and/or their agreement with the idea that the Democrats also have the more Biblical position on certain Issues. Their choice for the GOP is largely based upon the Moral Issues which they have deemed more important than Economic Issues.