So this will be me spitballing a few things out before I get to the thesis as it were.

We know that Roshar was created by adonlasium, and that by a function of that spren and the prexisting biological life existed as well.

We know that typically that all people who take in investiture magic typically are more easily granted this from having cracks in there spirit web, ie suffer some form of psychological strain, trauma or otherwise

So it makes wonder we’re the creatures that adonalsium let evolve upon this world designed to be able to accept magic better, as opposed to Yolen humans? As of so far we have had no examples in the cosmere of base uninvestited people having there cognitive and spiritual awareness via rhythms.