Because some critics are finding a way to criticize the Lakers. That treatment to Westbrook isn't that harsh when he was playing in Houston Rocket and Washington Wizards. There are just of people who don't like Lakers and Lebron James that's why these people are finding a way to always throw a bad impression at the whole Lakers. There are lots of issues that the Lakers faced but didn't highlight.
Anthony Davis, an injury prone, didn't even receive some backlash for being soft. Westbrook can't carry a team while AD and LBJ are not present.
Other than that fact, the people and the fans really expected the new roster of Lakers to be so dominant last season because the team are consist of All-Star players when in reality most of that All-Star player is not in their prime anymore. Moreover, they set up a high standard for Westbrook with almost no room for mistakes because of the stats he had in the past years.