It's like dialects and accents in languages. You learn what you grow up with, particularly from your family. And even if you learn new languages, it's extremely difficult to break through your original accent/dialect, like the way you pronounces vowels and consonants.
Think of how the Japanese or Russians pronounce English words. even if they're extremely fluent, you can still hear parts of their mother language being brought over.
I am in love with this "Westerners drawing Manga" analogy. Goddamn it's beautiful and explains so much.