Non-native English speaker here, to me “maintain cleanliness” just feels a bit formal compared to “keep clean”, but doesn’t feel incorrect at all. It makes me wonder how many phrases the I speak/write feel incorrect to native English speakers.
Generally speaking, native speakers need to get over themselves. English has become the global language (which no-one got to vote on) so native speakers should accept local forms and foreign influences and invasions, especially since English has been doing that since its inception.