Just in the usage being complained about argues that whatever it is modifying does not need or benefit from analysis.

It just creeps in, but why? Why does it creep in? Often because we do not want to do the complicated analysis as to why things are the way they are because then it does not validate our preferences which are often emotional and not movable by logic anyway.

Just exercise more, fatty, says that the problem of being a fatty has a simple solution that anyone can see and there is no need to argue the point here. Start jogging!!

Just in the rather archaic meaning nowadays as being right and proper and what should happen in a fair and balanced universe is tangentially related, the archaic meaning of Just is memetically echoed in the assertive mode of Just doing things. If the world was fair and balanced and most of all really simple then Just jogging would cure the fatty, but it doesn't.

on edit: changed than to then.