While I cannot speak for all evangelical Xians, the reason I like free markets is because I like the “free” part. I do not know if this is more prominent among evangelicals, as opposed to other religious groups, but I like freedom and would rather error on the side of too much freedom than too much coercion.
There are ways this blends well w/ Scripture, for Jesus is Lord – which implies that Pharaoh is not. And it seemed important to G-d to demonstrate that.
(I know, G-d has given certain legitimate functions to government, but normal humans being what they are often go beyond the boundaries G-d intended. I think of Matt 23 where some who had legitimate authority were still chastised…)
I am also moved by how freedom glorifies G-d. The Adversary challenged that Job served G-d for the pay. Without freedom, the Adversary could claim that we only serve G-d because we do not have the opportunity or ability to do otherwise.