Skins used to be only available through money. Orange Essence is a way of getting free content that didn't need to be made available. Sure, it's not as fast or as easy as some would like, but it's supposed to be a perk that Riot sacrifices some income to give to players, NOT a replacement for actually buying content. This is why it's randomized, and why you can't buy every skin you get but have to pick and choose which to disenchant for essence.
Frankly, earning essence by disenchanting skins is strictly superior to gaining random amounts of orange essence and fewer skin shards, as then you'd have less choice of shards.
If I get one shard and 1000 essence, I have one choice of skin. If that 1000 essence comes from disenchanting six shards, then I have a total of SEVEN skins to choose from, and I can disenchant the ones I don't want to build the one I do want.