Petty jealousy. Plain and simple. The F-35 is a technically ambitious project to the scale that for now NO ONE ELSE, including Russia, have the technical balls to attempt even on paper, let alone production, and every major aviation power in the world know this.
Most people here have never felt the recoil of a .22 caliber, let alone know what it is like to stand next to a nuclear bomb. Most people here have never been in a worn cockpit of an F-16, let alone know what it is like pulling 9gs in one. Most people here have never sat in a hours long planning session for an air refuel training mission, let alone know what it is like to go hard ride TFR over the water at 50 meters altitude.
What else can they do but to latch onto every single technical issues, of which nothing is immune from having, to try to make the aircraft the failure they wish it could be. Notice the more technically behind the country from US, the more noise those people make. Their oft 'I knew it...' is a symptom of that envy, as if they speak with their mouths from years of personal experience in aviation instead of the stinking farts they expelled with their anuses from last nights' meals.
