I can confirm that Purple 300 (Lvl 5) Slicing missions also return HALF the mats.
And I know why.
FREE TO PLAY
Don't have enough Purple mats? Buy some in the CARTEL COIN SHOP!
Maybe that you are not that far from truth. Probably this is another change aimed toward F2P, we still don't know what limitations F2P players will have with crew skills. If they have full access to gathering but limited to crafting this would have caused an inflation of materials, so they limited it now. The rich/bountiful thing is a bug.
Just a theory, and i would really like BW/EA to tell us something about this.