I'm conservative, ironically enough. I think it might have more to do with upbringing then? Or maybe I'm the exception.
No, it's a bit more complex than that. Let me see if I can explain why this topic is so fuzzy.
First, you take people, complex fuzzy thinkers, and find some tendencies (in MBTI 5 of them for each axis). Then you average them out and you get a trait like N:S. Then you take those and ask them a bunch of questions about political leanings, of which are defined broadly and subject to social considerations (ie: ask what liberal means in the US vs Europe). Then you take these two, compare the two, and find out that in general, N prefer liberalism and S conservatism, which are political definitions made up of the particular questions that were asked.
So... yah. The OP posed it well, actually. It's not a matter of "being liberal", but of being "more liberal". That is, there is a preference - one side "shifts" towards the other.
Why is this important? Because the majority of Ns could be liberal, and Ss could be most conservative
and there would still be more S liberals than Ns. (If you accept about a 70% population for Ss, then it would be ~35% to ~15%, actually).
So yah, just because there is a correlation does not mean it can be generalized to the overall population.