Our ancestors evolved in a world that was periodically drenched in magic, and until the Anu in their genetic meddling severed our connection to the world around us, humans worked with magic naturally.
Over the tens of thousands of years of being hunted, abused and enslaved by the Anu when humanity was still very young, those with strong intuitive abilities had a much better chance of surviving. They might predict airstrikes and gather intelligence (sensers), hide an encampment and affect the landscape (sources) or cause events to fail and succeed at will (shapers).
Because of the abuse in humanity’s childhood, magical abilities became widespread, when otherwise they might have remained a rarity.