No politically correct way to say some things.
Could it be that people speaking (for example) English as a second language simply don't speak it as well, regardless of accent? I'd think they miss some of the crucial distinctions and oddities that make it possible for us to separate near-homonyms from a native speaker. Further, it's well known (to speech researchers anyway) that most people don't actually "say what they say" - syllables run together and so on - this was a major problem initially in speech recog (which was a field I did a lot of time in). Humans, unlike computers (at least then) make _extensive_ use of context to overcome this and related issues when "understanding" another's speech (which is far more to the point than mere recognizing, when even a perfect transcript would have those missing or run-together syllables).
The "not pronouncing what you thought you said" issue was a huge eye-opener for many workers. It's easy to perceive it now due to non linear audio editing tools that let you examine small excerpts, though.
Further, when the speaker is "thinking" in their base language, they use grammatical constructs native to that language but not English, which tends to defeat our human predictive understanding, or "sounds to meaning conversion".
I know that even I have some issues with strong accents, and also that even long time exposure to same doesn't overcome them. I'm no longer in the field, but I'd bet an analysis along these lines would bear out these observations.