Algore started this
Not really, but almost. During the Clinton administration, Al Gore headed up some sort of government efficiency tasks force or the other. One of the things that they did was change the chart of the USPO. Before, it was "Issue all valid patents." After, "Help our customers get patents."
So the validity of a patent became something to be litigated as a matter of course. Anyone holding a patent needs a team of attorneys to do so. So much easier to just sell the thing off to an NPO. And one small step from NPO to patent troll.