I think that most strongly political people are willing to compromise on some issues but not on others. Different voters have different lines in the sand that they draw. For example, to somebody who is willing to compromise with the Left on immigration but is unwilling to compromise on social issues like abortion, I may seem like a "single issue voter" for rejecting a pro-amnesty but solidly anti-abortion candidate. Conversely, to me the anti-abortion activist who refuses to vote for a candidate who doesn't feel strongly about abortion but takes a hard line on illegal immigration may seem like a "single issue voter."
That has been my experience. Put enough folks together with their own "single issue preference" and you end up with millions of votes lost over a dozen different "single issues"
Some folks may be (for your specific area) pro-life, but they don't say it strongly enough and use it as a main part of their platform and many will still pass on that candidate for "being wishy-washy/weak/etc." even if it means that a abortion-mill, "kill them all" piece of Evil like Obama gets another chance to help insure millions more are killed. I can understand the concept of being fussy with one's votes, but have a bit of a problem when the difference of choices is crystal clear and the choice that results in the most evil is the one taken.
But I digress - different season and different candidates. None of our main choices are pro-abortion.