However, soccer is a little different. It is customary that players sing their national anthem in international tournaments. Is it a huge deal the American women mostly didn't sing? No, but it is notable in the larger context of international soccer.
National teams ARE professional sports teams outside the Olympics. They are paid to play. And in most sports there are often members of the team who “transferred” to the country either because their home country didn’t pick them, or because their home country isn’t any good at the sport and they want to win. International sports is rife with people “representing” country X who weren’t born there, don’t live there, and mostly never go there.
Every country has their thing. America’s is into the game face for pre-game anthems. Singing is for winners at trophy ceremonies. So no it’s not notable. It’s not a deal at all. It’s just people looking for reasons to get mad.