its the same as with their nationality. really, like its something to be proud of, wtf?
Turkishwarrior93
AmericanSniper55
brasilelitefighter
etc....
actually there are psychological reasons for this. its group dynamic and scientifically kinda proven. you can take a room of 20 people and split them into 2 groups without any meaning, and they will feel entitled and related to their own group, despite the fact, that they only are in that said group by chance. theyll also rate their own group as superior and better and the right one....
the same could be said about nationality and race and religion. (while you also add nostalgic/upbringing factors...)