I don’t think it takes a large number of the population to practice something to get a class for it. Take the Shendralar Highborne who rejoined night elves. Now they have the option to become mages. The Sin’dorei are always looking for new ways forward for their people and to not repeat the mistakes of the past. Their page on the worldofwarcraft race page has some interesting wording suggesting they are looking for alternatives to arcane.