Because Paris St. Germain comes from Saint-Germain-en -Laye, Red Star and Paris FC are the historical clubs from Paris(75). Marseille and Lyon are particular, it's two football cities, though Rugby is big in Lyon too, but they don't represent the south, they are the exceptions not the norm. The north is mainly about Football and the south is mainly about Rugby. And it's not the people that don't care about football that crititicized Pogba it's the one following closely football, the ones coming from cities like Lyon and Marseille.
The reason some people had an issue with Pogba in France is exactly the same than in the UK, pundits talking nonsense, complaining about his haircuts and why he isn't Vieira or Zidane.