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.
I like to think of spells like eldritch blast as being a set of mechanical rules for explaining things which may or may not be the same thing in world. Two warlocks of two different devils might be casting it in much the same way, firing a red and black beam that gives off the smell of brimstone. But maybe a fey warlock’s EB is a bright cyan with the smell of freshly-cut grass, and a GOO warlock might cast eldritch blast with a deep purple.
Sure, but even then it doesn’t make a lot of sense that all the different ways that Warlock patrons can present themselves, that they all are great about giving people raw damage potential as a cornerstone of their pact, regardless of how you flavor it.
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.