Social Conservatives provide the same sort of energy for Republican candidates that the public employee unions do for the Democrats. Recall that Bush almost lost in 2000 when on the eve of the election they Democrats sprung their little drunk driving trap. Lots of people who saw Bush as a “church” types stayed home because they felt betrayed.
In any case, it is because Republicans have thought the way you do since Reagan’s time, that it was enough to give lip -service to the pro-life cause is the problem.
They pick up their marbles and went home the first time the opposition threw a little dirt? Yeah, that's just the kind of "energy" I want behind me....