Why aren’t humans in The Lightning Thief more aware of the activities of the gods?

Percy Jackson and the Olympians: The Lightning Thief is an installment in the Percy Jackson series written by Rick Riordan. In this particular installment and in the series as a whole, humans are unaware of the affairs of the deities and demigods, except for the main characters and mortals who are demigods.
This is because the gods and demigods conduct their activities "behind the veil." This means that humans will interpret mysterious phenomena as natural occurrences. For example, hints of a cosmic war in the sky between the gods will be interpreted as a lightning storm.
Another reason mortals are complacent or unaware is that the Percy Jackson stories take place in modern times, when people are caught up in the affairs of their daily lives. This is similar to the simulation featured in the film The Matrix, where humans live within a controlled sphere whilst the "true masters" of the universe and reality conduct their activities outside of this sphere.