The question should rather be why they implemented the Dye Slot system in the first place when instead they could have implemented a coloring terminal similiar to the Appearance Designer where one can change colors on their items via a slide. People would then have to pay per color, but at least every color would be available to them, in whatever combination they wanted instead of having fixed color packs. This would have been so much easier. Even DC Universe Online has this for Christ's sake.
I agree that the Dye system is flawed because of the rarity of some of the colours.
Unfortunately I also forsee a s**tstorm if they ever change it because of the people who have spent millions of credits on buying that one rare dye (Because you know that there are alot of people out there who only buy stuff because it is rare so they can show off)