There are devils who scheme and wheedle souls. There are beings of ancient wills and unknowable intent. One may even have entreated elemental forces from the primal dawn of the world, or Genies who have within them a stunning variety of desires, wants, and whims. Alongside Archfey who encompass a dizzying variety of the beliefs and motivations. What unites them all?
They all think Eldritch Blast is a pretty cool spell.
To be fair, in 5e it’s not automatically granted to every warlock. It’s a cantrip the player can choose to select or not, which implies not every patron grants it. It’s just very popular among the kinds of people who seek out patrons for the purpose of becoming adventures.