Even though he already had a pill furnace, Mo Wuji still couldn't concoct god pills. Forging equipment was different from concocting pills. When it comes to forging equipment, even if you only have one material, as long as you had your own Equipment Dao, you could forge a magic treasure. The greater your understanding towards the material, the better the magic treasure forged. Thus, if your understanding towards the material was shallow, then your magic treasure would come out rather ordinarily. It was exactly because of this reason that Mo Wuji's low-grade god equipment were very ugly.
On the other hand, when it came to concocting god pills, one would need to have a deep understanding towards the god herbs, their unique characteristics, as well as the pill formulas.