This is a broken link - commonly seen as "404"
Follow along here for other IT issues
and escalate this one to customer care or wherever you think will get more traction. It's a simple "housekeeping" chore to remove a broken link or even a top level menu item if the Stewards program has really been retired for good.
As to the original question on this thread, the Insider Stewards program no longer exists.
Here's some info about how it used to work.
"The Insiders Stewards program allows our most active and knowledgeable members to have a formal leadership role within the Insiders community. As community leaders, Stewards help drive positive participation throughout the site and answer questions from other members so the site remains a unique resource of travel and Marriott Rewards information.
The Insiders Stewards program is comprised of five Insiders, who may communicate with Marriott to show their understanding of community trends, receive feedback on issues, collaborate on site improvements, and share important previews that they then can share with members. By taking an active leadership role within the community, Stewards help reinforce the purpose of the Insiders community: to ultimately provide a community for members by members."
Now there is a team of community moderators that handles the duties once performed by the Insider Stewards.