I don't see why. A lot of Western Poland used to be German, and it's not like there's one German cuisine either. You don't get many Bavarians eating pickled herring with beets, but's it's classic cuisine in Berlin.
Western Poland used to be German, but all the Germans left/got expelled. After WW2 it was resettled with Poles from Eastern Poland, nowadays Ukraine and Belarus. Which makes traveling from Berlin to Poznan or Wroclaw an interesting experience. Directly at the German-Polish border, you'll enter Eastern Europe, then when you arrive in the mentioned cities, you're suddenly back in Central Europe.
Also, you'd be surprised at how widespread pickled herring is in Bavaria. Herring has been a trading good for millennia in Europe, was and is still consumed in the winter months in Bavaria. You can easily get a "Fischsemmel" at the Oktoberfest in Munich. Bavarians also used to pickle everything for the winter: cucumbers, beets, cabbage, beans.
I know you can get herring in Bayern, and I know you can get a Weisswurst in Berlin. That doesn't change the fact that they're represented differently in the regional cuisines.
The cuisine up here in Berlin/Brandenburg is much closer to that of Poland than it is to that of Bavaria. I say that as a person who lives in Berlin with Polish roommate, and travels pretty regularly to visit friends in Munich.
You can also get jiaozi and tempura shrimp at the Oktoberfest, that doesn't make them traditional Alpine food.
> Directly at the German-Polish border, you'll enter Eastern Europe, then when you arrive in the mentioned cities, you're suddenly back in Central Europe.
I mean I get that impression even before crossing the border to Poland. It's just very rural and not exactly wealthy on either side of the border.
That about sums it up. If it weren't for the Oder river, it would be hard to tell where one ends and the other begins. There are some places on the border where the only signs that you've changed countries are... the signs. (Specifically I'm thinking of Gorlitz/Zgorzelec.)
Also, you'd be surprised at how widespread pickled herring is in Bavaria. Herring has been a trading good for millennia in Europe, was and is still consumed in the winter months in Bavaria. You can easily get a "Fischsemmel" at the Oktoberfest in Munich. Bavarians also used to pickle everything for the winter: cucumbers, beets, cabbage, beans.