What's the problem? Looking at the electoral map of modern Poland's borders, outside of Warsaw the left wing guy was supported by areas formerly known as Prussia, while the more ancient ancestral lands of the Poles voted for the right wing guy. Maybe you guys should just reverse annex yourselves and give the krauts their old clay back.
the history was much more complicated, by
"areas formerly known as Prussia" was also the land of Poles occupied by Prussia for a long time.
The other half od the land of Poles was occupied by Russia.
The Germans were always more advanced people than Russians, so also the polish area of German empire was better developed than a polish area of Russian empire.
Better infrastructuere = more money = less support for socialists
Also its easier to make trade with western countries when you are more west on the map. That means more EU enthusiasts.
There are no Germans in western Poland, the people who live there are often people who after the ww2 moved from today Ukraine and maybe Belarus etc.
Nearly 100 years passed since WW2, there is no giving any land back to Germans after that time, especially since this is was a kind of penalty and repayment for starting WW2 and damage nazists done to Poland.