As an ESL I can tell you that it also depends on your exposure to English. Non-native English speakers are often taught and exposed to mostly (classical) literary works and/or formal speak (for example, math and science). It's one of the reasons why their speech might sound stilted in person, but "perfect" in writing. What you think is "colloquial and limited" might be considered "perfect native speak" by the ESLs who often don't get that kind of environmental exposure to English.