Why not just make Blue Essence Purchasable with IP?

I mean, right now if you need Blue Essence it's simply a matter of buying a bunch of Mystery Champion Shards with IP and then converting them to Blue Essence.

Why not just skip the middle man and allow players to buy quantities of Blue Essence (either find a fixed IP value per Blue Essence, or do it in Tiers where spending more yields slightly more Blue Essence).