I think what is meant is that those loyal (20%) Coke drinkers will continue to drink Coke regardless.  There is no reason to focus on them.  You are also probably not going to be able to convince someone who never drinks Coke to start drinking Coke.  There is no reason to focus on them.  That means the best area for marginal sales is those people who occasionally drink it.  Getting those people to choose Coke slightly more often is probably the most efficient way to increase sales and is the method around which Coke builds its business.