Evangelical does not automatically equal conservative. Just look at Huckabee for example. There is a major segment of the “social conservative” group that loves big government as long as that big government is doing “Christian” things.
There are millions of evangelicals who are fiscal liberals.
They don't label themselves as such but when they hear "the Gov't wants to give money to the suffering and underprivileged" they wrongly believe that message to be christian compassion.
These evangelicals are not smart people. They are led by a bleeding heart, not their head.