If you look carefully on the pages where fantasia are sold, it states that each option can only be purchased once. To recustomize more than once, you'd have to buy increasingly expensive packages containing greater numbers of flasks. Clearly they only begrudgingly support character re-customization.
It's not like they don't already have the ability to change a character's name. The feature is built into server transfers and so isn't a major issue to implement (they'd just copy all the code used in that and spend at most a few hours getting an alpha version of the product ready).
The reason character re-customization is an option in other commercially available MMORPGs is because many people DO NOT have time to reroll characters. Its a way to make their character look like something else when they grow tired of it. Under no circumstance does it encourage players to invest more hours on new characters. If they stop liking the way their character looks and they do not have the time to reroll, they aren't going to be making a new character. That's purposely engineering a reason for a time strapped player to stop playing.