Why are all the main characters in this film NOT Scottish?

I enjoyed this film but I have to say it irks me that a film made in Glasgow chiefly only has Scottish actors in minor roles.

It suggests to me that the kinds of problems of work, sex and relationships cannot really happen to Scottish people and they should only appear in films as alcoholics, drug addicts or people who suffer from other social problems as most Scottish films do.

While listening to the dialogue I think some of it would not have translated well to Scottish voices but I remember being young at the time when the film was made and recognized a number of the issues and problems that were spoken about at the time by me and my friends.

It is a little annoying.