Not to go on-topic or anything ;), but "out of the loop" is a computer programming concept that emerged in the late 40’s out of Alan Turing’s pioneering work.
A ‘loop’ is a bit of logic that essentially says "Do <this> until <you’re done>." <THIS> is frequently a very complex task, and <YOU’RE DONE> is a check to see if the task needs to be done again (usually with different input data).
In nearly every interesting software system, all the action happens within a loop, usually in a loop nested in a loop nested in a loop. Code that is ‘out of the loop’ is mere housekeeping.
Thus, by inference, anyone who is ‘out of the loop’ is marginalized in a social or organizational sense. S/he is not in there where the interesting stuff goes on.