I think people keep forgetting that manga is made in Japan, for Japanese people. It would be weird to have Sonic tm, Whataburger tm or Arbys tm. Having Japanese food provides something relatable to the intended audience.
And it's not like people are shaming other foods or saying how they will never eat non Japanese food again, it's a novelty to people who have never had foreign food before, you get similar reactions in reality just less exaggerated.