Because they are "not the same banderites". The modern use of the slogan managed to get heavily rehabilitated over years, also it originated considerably before conflicts (increased by polish fascists who effectively took over sanation government) led to massacres (which happened both ways, and similarly current polish government essentially does the same thing as Ukraine with Stepan Bandera, arguably longer - it started before they got into full power).

And well, we're next if Ukraine falls, or such is the feeling among considerable portion of polish people. Even pure self-interest makes it clear which way our support is going.

Wołyń was horrific, but the Ukrainian people today are quite obviously not the same people as the banderites 80 years ago, the world has changed much since then. This rhetoric only serves Putin's interests, who must be quite displeased with how accepting Poles are of Ukrainian refugees.

PS I do wonder why your Polish is broken, it should be "banderowców którzy", not "banderówców które"