1) Many think the best way to make foreigners understand is to be chatty and informal.
2) Anyone wanting to get to the top of international business, medicine or academia (but possibly not sport) needs to be able to speak English to a pretty high level.
3) This may seem friendly but, as it probably involves using colloquial expressions, it makes comprehension harder.
4) Equally, any native English speaker wanting to deal with these new high achievers needs to know how to talk without baffling them.
5) Because so many English-speakers today are monoglots, they have little idea how difficult it is to master another language.