They dont do this to allow people that dont want to gather or craft and are outta gill to farm 30min lvl 1 shards and make 20k gil. In fact i know at least a dozen players that refuse to craft or gather or do w/e and just farm instances till they are out of cash in which they go farm some shards to sell.

And since high end crafters will not waste their time gathering this stuff everyone buys it from the market. Now if they allow breaking down higher tier elementals to lower ones i could go farm a few clusters with my lvl 50 DoL and i can make with the above schematics 100 Clusters = 500 Crystals = 2500 Shards in like no time afking the spot in Mor Dohna. Hence making shards super cheap and easy to get rendering them useless.