Poland has a checkered history. It sucks being a big, flat place between the Germans and the Russians. Armies love flat places. Then after WWI being between Germany and East Prussia wasn't good either particularly when the Poles believed the British guarantee was worth a bucket of warm spit and refused the Germans passage through the Corridor.
They just never learn. When a major power says 'we've got your six' you'd damn well better have Plan B oiled up and ready to go.