Because it rhymes ?
I would guess so.
BTW, thanks for the pic. There is a Brazilian
player in Korona Kielce, it seems, and some fans don't want him for some reason. In this case, they are calling him Murzyn because of his darker skin, not because of his ethnicity. Someone picked the word "Murzyn" because it rhymes and conveys the meaning that the "poet" wanted to convey (we don't want the dark guy on our team). Unfortunately, you cannot forbid anyone to use any word, including neutral or positive terms, in a negative context.
Down the road from me there's a wall with 'Murzyny do drewa'
I hate to nitpick, but that's not Polish, not even slang Polish or uneducated Polish. So maybe, if you make mistakes like this when quoting graffiti, your command of Polish is not that great after all, and some nuances might escape you?
Speaking of introducing language change, what do you think of this:
Do you think this is a legitimate process?