Why Do Some Teams Take The Knee And Some Don't?

In football, Over the past year or two, you must have noticed
players taking the knee just before kickoff in football games.
And you also probably already know they do that in support of the
fight against racism and discrimination.  Of course, the
English players took a knee before all of their games including
the final in Wembley. Wales also did; Belgium, too. 


But the rest of the national teams either did not take a knee at
all throughout the tournament or did in only a few games.
Understand the reason behind it, we know it is for racism, but do
the teams that don't kneel don't know about racism?