Because its not worth it
I craft tons of implants of any level (21,25,29,33,37,41 and 45) and anything below lvl50 is a waste of an augment slot cause noone will augment or use an augment for an implant while they are leveling
Even BH implants with augment slot the price difference is not even worth it cause you sell maybe one or two a week if you are lucky
Even Hazmat implants they are so expensive that again 60 k more or less is not gonna make you turn around when the implant goes for 1.7 m and you might see just one or two at the market if you are lucky
So basically the whole augment slot for implants at any level doesnt add anything, much better would be to have another implant made, that way it would be actually worth something to have a crit
I've sold plenty of augments of below level 50. Granted, I was only crafting them to level up but it appears that PvPer's looking for an edge and players power leveling are more than willing to shell out credits for augments.
What you won't see are people paying extra for an item with an augment in it from a crafting crit. Too many times I see people listing sub-50 items with augments for twice the amount a non-augment slot item sells for. At the most you should only be adding what it would cost normally to put an augment slot in since most people have plenty of low level augment kit components laying around.