Why are there multiple grades of glamor prism?

[ChameleonMS]

The original goal was, IIRC, to prevent you from glamouring a high level item on to your low level character. But, the game already has a secondary check built-in to prevent this.
E.g. Job is lv42 attempting glamour a lv46 item. While the Job level meets the Grade 4 requirement the Job level does not meet the item level requirement and the glamour is prevented.
Why they did not just make one universal glamour for each class?

Time to guess:
To limit market flooding? Although this happens any ways, there are currently over 200 Grade 1 Weaver prism sellers, each with 3 to 5 per stack on my server right now.
To be overly complex? This is an MMO and they do odd things like that.
To force people to selectively purchase them, instead of stocking up?
To bloat our inventories? As if we did not have enough of that already.

[Mjollnir]

Time to guess:

Initially designed it one way, but the way it was eventually confirmed was slightly different and now it'd be more work than it's worth to simplify it.

[DarkDedede]

Time to guess:

Most likely because they haven't bothered to do anything about it yet.