(Full disclosure: I had stretched earlobes in the 90s, big enough to stick a thumb through. But I was never really into piercings and had the lobes repaired later.)
There's obviously a lot of overlap with people who are into tattoos and those who are into piercings. A lot do it to be trendy, fit in, stand out, whatever; I'm not going to engage in the "what do body mods MEAN" debate, there are other threads for that. But I will say, ime, there's a certain kind of person who is REALLY into multiple piercings and/or stretching of lobes. They're the kind of person who always wants something to mess with, fidget with, work on, etc.
This urge often extends to their personal life, there's always some drama, some issue, someone they're trying to to fix. When you stretch your ears, it's a long ongoing process you can be working on for years. Every time you do it there's a little pain and a little victory. You get to buy new jewelry for it, care for a little wound.
Among normie women, it's the same type of urge in the one who is obsessed with having her nails done (beyond just wanting to look polished and professional.) I think the drive comes from a place that's usually pretty harmless and normal, maybe a little neurotic but not a big deal, if you're just into manicures or whatever.
But I honestly think it's on a whole spectrum of behaviors, the far end of which is stuff like self-mutilation, pooning out, Munchausen's, etc. (Just like saving some paper grocery bags and rubber bands is totally normal- but the far end of that urge gone haywire is behavior like hoarding.)
Anyway, all that is to say that I think pooners are not just doing it for the look or because it's a goofy subcultural thing, like some people. They do it because they simply cannot help themselves. They're doing it because it's an itch to scratch, an urge they have to take control, to change themselves, to physically and visibly transform. Something to work on, with ongoing and increasing results, but which, unlike going to the gym or therapy or school, takes no real effort or character to achieve.
This ^ is also why they seemingly endure endless complications and revisions with their rotdogs. It's why women who say they have no dysphoria lop their tits off. And it's why while many of them have tattoos, those aren't their main thing. Those are literally only surface level and by definition unchanging. The ears are more appealing as a visible deeper change, before they move on to pooner-centric mutilation. They are happy with never-ending painful projects to fuck with until they finally burn out from their 40th rotdog fistula UTI and 41%.