We have no idea why people pronounce it kwibec.

Because in English 'qu' is pronounced 'kw'?

You are right that qu is generally pronounced kw but as we now see - not always. As with any name you try to pronounce it correctly. With an unusual spelling or sounding name people have to be corrected/informed, that is true, that is why they turn to a dictionary. You'd think the dictionary would try to get it right. People rely on a dictionary to be accurate.