The reason is -- and I have come to this conclusion after a lifetime of interaction with people of almost all faiths and writing about and studying religion -- theology does not appear to have much impact on people's values. Liberal Christians and Jews share virtually no theological beliefs yet think alike about virtually every important social value. So, too, conservative Christians and conservative Jews share virtually no theological beliefs, yet they think alike about virtually every important social value.
Meanwhile liberal and conservative Protestants are in agreement on theological matters -- both believe in the Trinity, in the Messiahship of Jesus, on Jesus being the Son of God, on salvation through faith rather than through works, and more -- yet they differ about virtually every social value. Obviously, shared theology doesn't create shared moral or social values.
Or take Judeo-Christian values. I have written 24 columns explicating the meaning of Judeo-Christian values, yet never once used the term "Judeo-Christian theology" because there isn't a Judeo-Christian theology. Judaism and Christianity differ on most of the major beliefs of Christianity -- the Trinity, the place of Jesus, whether the Messiah has come, the nature of salvation, and more. But they share almost every important social and moral value. Once again, the relationship between shared theology and shared values is next to nil.
Therefore the theological beliefs of a public figure should matter only when one is choosing a theological leader, never a political leader -- unless those beliefs form the basis of social and moral values that one abhors. It is very important to know the theological beliefs of one's clergyman or the head of one's seminary, but as far as the head of one's country is concerned, only his moral and social values matter. I would much sooner vote for an agnostic whose values I shared than for a believing Christian or Jew whose values I did not share.
None of this is an endorsement of Mitt Romney's candidacy or of his values. It is an endorsement of the irrelevance of his theological beliefs.