Recently on Reddit, somebody mentioned that Autonomy's investure doesn't empower sapient beings directly.
1. On Taldain, the sunlight contains investure that energizes microscopic lichen in the sand. Sandmastery is the manipulation of these organisms, but as far as I can tell, involves little to no flow of investure through ones self.
2. On Patji, Avien are formed when normal birds eat the grubs in the Eye of Patji. Notably, there is no effect if a human were to consume said grubs.
I believe that this is intentional on the part of Autonomy, and I believe that I know the reason why.
We know from Oathbringer that Autonomy is leaving sentient splinters of herself around the cosmere. From Secret History, we know that a share cannot be taken up without significant connection to it.
As there is more Autonomy to go around, the likelihood that someone could eventually take up a splinter is higher.
Autonomy tries to limit others connection to it, either as a precaution or simply due to her intent, by providing this buffer between her magic and the people of the cosmere.