I agree with Pentrep.
Think about it this way, while they would make some money off of class change tokens, people who do end up wanting to try different classes and are willing to buy them would take away one of the things that would likely keep them playing the game....trying out the other classes you might like. If you like a class enough then you should be okay with leveling the character up, whether you have already played through the story line before or not. So in my opinion while it ends up getting the company a little bit more money, they would likely end up losing a good amount of their player base sooner due to becoming bored with the game from having tried all of the classes at an earlier time.
If they happened to have class change tokens then they would have to bring in new content to the game at a faster pace in order to keep a huge portion of their playerbase, and if they did that it would likely mean more lower quality content. Creating and getting new content ready to release takes a lot of time and money, especially content of good quality.
There is also a level of impulsiveness when considering racial or class changes. There are many people who don't actually think about what their doing before they do it, then regret the decision later. If you implement racial/class change vouchers then you weaken the power of making firm decisions. I understand people change their mind, but at some point the user has to be held accountable for poor decisions.