This is a variation on bunch of Ti/Fe/Fi/Te posts there always are but I haven't seen this exact question asked, sorry if it has been.
Anyway, everybody uses and introverted and an extroverted judging function. But why? Actually I think my question is clearer if MBTI terminology is avoided so I'm going to try to do that—you might not like the way I define the functions but please interpret that as me expressing myself poorly rather than me understanding them poorly. And so the question is:
Why does logical thought motivated by no practical objective, pursued for its own sake, tend to go hand in hand with a flexible, relationship-based emotional attitude?
Why does an individualistic, resolute emotional outlook tend to pair up with goal-oriented logic?
That is, why does Ti always go with Fe and Fi with Te? But the answer's not "because everybody needs to use an introverted and an extroverted judging function", that's equivalent to just saying "because they do".
Since ExxPs and IxxJs have thinking and feeling as their second and third functions, they might the most useful examples for explaining this (as opposed to IxxPs and ExxJs, too unbalanced).