write 20 pages worth of words for a normal person's backstory?

Sure, they could.

But knowing that his favourite breakfast food is poached eggs benedict and he shits with his legs on the toilet rim is wildly different to knowing that he lost his parents because Jeremiah, his best friend and to-be-warlock, decided to make his pact with a demon behind the shed where Jer's childhood sweetheart Suzie, the blacksmith's daughter, cucked him.

20 pages of backstory for people that are on the cusp of being background characters in a roleplaying game is ridiculous and will definitely be filled with superfluous bullshit or reasons for why they have a ring of minor invisibility with infinite uses.