Quote Originally Posted by thenonsequitur
I think this is the reason.

I think they're thinking to themselves something along the lines of "lucky bastard--90% of the time he's bluffing here and I would have caught it with my pair, I got unlucky enough to call the 10% they had something". And of course they think that same thing the nine out of ten times that they lose their stack looking up someone's monster with middle pair. And they use the one time in ten when they pick off a bluff with middle pair to reinforce this fallacy.

So when they "get unlucky" and call your push when you happen to have a monster, they want to prove that they made a good move picking off your probable bluff, and that it was just luck that you had a hand this time.
That's so convoluted I'm surprised they can actually reason it out.