Clapping and putting on a polite face (doesn't have to be ecstatic just caring for others) is meant to support the person who DOES win, whoever that is. If even a quarter of the room is giving the stink eye because their friend lost, then it doesn't look like a great moment for the winner.
That's why the tradition is there, clap for the winner, cry in the bathroom. It's considered good manners.
Yes I also would have wanted to see her win, but for an old movie she did with Ralph Fiennes back in the day. And maybe Waiting to Exhale? or Whats Love.... I have a LIST! If she doesn't win for one film, it may end up being lifetime achievement. For me, as an actress, the SAG awards are what I care about.
Here is a far more serious offender, and yes, it was a big deal at the time.
