I would guess some folks are addicted to the race to the top, some smell a money-making opportunity, some probably get a kick out of doing their best to cockblock content (not as easy on TLP but still possible), some might take a chance to get in on a game they never really got to experience, and some just have an undying love of original EQ and do everything they can to recapture the magic of their first few months in an MMO.
I mean, I loved the shit out of my time on Phinny, had a grand time with some grander people and actually did manage to recapture some of that original magic. Shit, the first week I had a key to ST, I spent all day drinking and straight up passed out on my keyboard face-first about 5 minutes after I scored a primal. Come to think of it, I wandered through most of our raids either asleep or piss drunk. I was a bard though so it didn't really matter. #bardlife
No way in hell I would do it again though. One more time was enough.