It's because the player wanted more, but the DM (me) wasn't sure how to go about that because there aren't any tools provided, and the traditions aren't there to fall back on due to the class' newness.
It's been in the game for 23 years and three editions! That's almost half the game's existence!
But it’s based on traditions that go back at least 400 years. You should read up on Faust (Fiend, several versions of the story), Prospero (Fey, from
The Tempest), Dr John Dee (real person, Celestial). More modern sources:
Jonathan Strange & Mr Norrell, The Mighty Nien (animation, GOO/fathomer
), Baldurs Gate 3, Neverwinter Nights 2.
For GOO warlocks, the source is petty obvious, since Cthulhu is mentioned in the subclass description. But patron indifference is also mentioned, so it isn't a particularly a particularly good choice for players who want to have conversations with their patron. To tie it back to
The Tempest, you should check out the movie
Forbidden Planet. This kind of patron tends to shade into science fiction. Doctor Who has a lot of this sort of thing for example. The
Great Intelligence is your typical jerk patron who controls it's warlocks like puppets but is very limited in its ability to act directly.
But since it comes from your player, why not ask them to describe their patron?
A few notes specific to the text in the 2024 version: Both fey and celestial suggest the warlock might call upon groups of this kind of being, rather than a specific individual; the text for the Contact Patron ability suggest that patrons normally communicate through intermediaries until the PC is level 9. As with all class fluff, I would treat this as suggestions, not rules.