[Sans-Culotte]

So applaud them, because they are showing even greater reverence for the flag than the standers!

Nice try, but no. The announcer asks "will you please rise for our National Anthem?". Not rising by remaining seated or kneeling is showing contempt.

[the OlLine Rebel]

I understand that, but people BOW/kneel in submission.

It’s not our way, but that is historically and culturally - almost universal - what kneeling and bowing means.