That is it and in same vain, legendary members contributing to the forum and answering newbie questions is not also obligatory as opposed to what Op thinks. Those regular names we see here daily and weekly are passionate about the forum. It is not easy for some people who were here since 2013, 2014 or even earlier to still remain active. Most of the people who started earlier are no longer here.
It doesn't really make sense for a Legendary member who in 2017 and 2021 has managed to become a billionaire because of his investment would happily spend a lot of time replying to spammers here. They wouldn't because honestly now they would really appreciate the time to enjoy life in all its luxuries. They can stay here for any number of reasons, but I'm sure it's not for something pointless.
Reaching Legendary during the merit system is something that makes me feel satisfied and I am grateful that I succeeded, but the feeling will be very different from those who were already Legendary before the merit system. But if those users are contributors, then I believe the rewards they get today are much higher than their activity. Legendary is not the end, it's just the highest rank and every one of them should still care about post quality if they don't want to be called spammer or shitposter.