Because misplaced loyalty usually comes with emotional blackmail.Not perhaps my greatest regret but I wish that in my callow youth that I had dropped people in the shit more often. people who really didn't deserve their actions covered up or played down.
Of course it's natural that miscreants deny their guilt, we all would.
But the moment you start expecting others to lie for you, or pretend they've not seen anything, it's time for them to man up and own up.
It took me a long time to realise that mis-placed loyalty is not a good thing.