why teaching some IT people, doctors and accountants plus Germans (shudder) is a drag.
Poland and Germany are rules-based cultures and their attitudes toward language are rules-based.
English speaking cultures have a more context-based approach to usage. A lack of endings that clarify syntactic structure means that English has a habit of 'drafting' content-words (nouns, verbs, adjectives) in contexts where they lose a lot of the original meaning and serve functions related to discourse or even form-words (pronouns, prepositions, conjunctions, articles).
People has different functions now. The first is a content word that means something like ludzie or naród (among others); another is to create plural nominalized adjectives as in "Polish people" which has largely replaced "Poles", yet another is used in impersonal expressions "People say...." better translated as 'mówi się', że...' or 'mówią, że...'
Understanding that principle is far more important than always having the correct past participle form (which natives often don't much care about which is why so many irregular/non-standard participles can be heard in native speech).