Monthly active users in a vacuum docent mean anything. Facebook has 3 billion monthly active users but has zero relevance. Bluesky and Threads have no cultural foot print compared to X.
They are when major news outlets with 100+ years of history write entire articles based on their direction, or even just reference single tweets as justification for an entire opinion article.
Zero relevance to what/who? There are a lot of "older" people on Facebook who are on no other platform. Super useful for targeted advertising. X users are more likely to also use other social media like Instagram and TikTok. This is why companies can afford stop advertising on X without much issue.