Accountable for what exactly? You can look up any anthem playing for any sporting event in the US for DECADES and the vast majority of athletes will NOT be singing. That’s just not how it is here. So why is it suddenly a problem for the USWNT? They’re doing exactly what YOUR favorite sports team has been doing your ENTIRE LIFE (assuming the math works out). That’s the American sports way.
If you play on the national team, all the eyes are on you. And you represent your country.
Colin Kaepernick played for San Francisco so that was different.
And Megan Rapinoe is on the national team so we are seeing the women's national team as the anti-American team.
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.