I work with a team that spans native speaker to barely able to form English sentences, and communicating clearly in a mixed audience like that is really a completely separate skill from native language use.

For the ones with minimal English it's often clearer to use phrasing that a native speaker would say is obviously wrong, but matches their native language patterns. Or use simpler but not-quite-appropriate words.

And for the native speakers, the awareness (or self-regulation) to eliminate idioms and less common vocabulary is nigh-impossible for some people.