
I think a lot of the Dak animosity started in 2016 when pro-Romo fans thought that he would have led the Cowboys to a Super Bowl that season (they went 13-3 with a rookie Dak) but lost their first playoff game.
What they fail to remember was, Dak Prescott played lights out in his first playoff game. Threw for 302 yards and three TD's and also rushed for a two point conversion. Dallas lost 34-31 because the defense let the Packers out of a late 3rd-and-20.
No matter the QB the Cowboys have failed to play complementary football when it matters the most. Romo and Dak were the QB's so they are always the convenient target for all playoff losses.
If Romo or Dak made mistakes, THAT is what lost the game according to fans. Nobody talks about the offensive line allowing pressure. Nobody talks about Micah Parsons not getting sacks. Nobody wants to hear about corners or safeties blowing coverages, or the linebackers missing tackles, or the d-line getting blown off the line. That's not fun because it requires cognizant thinking.
When the Cowboys win, it's a team win. When the Cowboys lose, it's Dak (or Romo, depending on the timeframe being discussed).