Aside from the things you’ve already mentioned (*), it’s likely down to ego and a sense of achievement; even more so since the merit system was created due to it now not being simply a question of being a persistent poster, but rather more of being able to create decent content persistently (way different than before).

(*) The respect that you mention is a false impression, likely to be more present when one is fairly new to the forum (after all, Legendary does sound like something rather outstanding at first). Overtime, you get to consider the persona behind the profile, regardless of their rank.