Poles often don't wish to be reminded of their Eastern or Slavic roots,
One: in school they learned that Poland geographically belongs to the Central Europe - so they want to correct anglophones who generally have a vague idea bout geography.
Two: Eastern for them is assisted with Russia, they don't want to associated with that country. So its bugs them on some level, that feeling it enhanced by the morons who "think" that Poland is a part of Russia and there is no significant differences between those two countries/nations/cultures.
I personally think that because such a term exist due to the cold war heritage it could be wise and smart on the part of the Polish people to make a good use out of it. Like unite the eastern Europe around the three seas area. Cool, eh?
By the way Lyzko I diss you cause you came across as a fake person. All about you screams - fake. No offence.