Ignorance

I think that one of the biggest issues in this matter is that the majority of students don't actually know what "accent" menas and, consequently, the ignore the existence of different accents when speaking the same language. The first thing teachers must do is, as I see it, is having students know what an accent is and, later help the students be aware of the actual existence of those accents by using realia such as audiovisual material, etc.