I have a guy in my group who is unashamedly a power gamer (which is fine by me, he still will participate in all pillars of play; he just always prioritizes mechanical power). His PCs consistently have some edgy loner backstory. I honestly think it's because he doesn't prioritize backstory when creating characters, instead trying to come up with a backstory which justifies all of the mechanical things he wants his character to have. The thing is, I've seen him RP fun or interesting character ideas for like one-shots, but for longer campaigns he always reverts to the safety blanket of an edgelord.

Recently he was rolling up a new character, and after he gave me the character sheet, it inevitably had some edgy loner backstory where the only details were things that explained his class, background, and proficiencies. So I politely suggested we workshop the backstory under the guise of working in some details relevant to the campaign. What I then did was talk him through his character's whole backstory from childhood through to adulthood giving him an opportunity to think through the backstory one step at a time, occasionally prompting what might be choices his character would've had to make at different points in his life.

The result of this was that he actually had to think about his character's backstory and it ended up being a way more interesting character concept.