What ItMe said. Unfortunately, there's just less purple for human eyes as it stands.

Though they obviously haven't used every shade of purple that there is, so we definitely could have more dyes. My guess is that they take time to add in what's deemed most popular, and just sorta sit on the other dyes... though there are so many brown dyes hehe, and I hardly ever see people using dyes in the brown tab.

I tend to gravitate towards Charcoal grey, Deepwood or Morbol green, Rhotano Blue, Wine Red, Gloom Purple, or Metallic Silver myself.