As Steedie said, people spend a lot of time just posting on yammer (or at least you can easily spend time doing it if it's a busy set up). As someone that doesn't use facebook, or social media in general, I find it quite pointless as if I want information I go to the intranet, or speak to people that know about the subject (I like speaking to people).
what's funny is that there was a push in one of my companies for senior leaders to post more on there and be more engaged - whereas in fact staff much preferred senior leaders to see them face to face or in a townhall setting or out on site or whatever. Ok during covid lockdown it was a good mechanism for idle chit chat, but I don't think there's any productivity gain - it's a good social outlet, but unneeded if you have other collaboration tools, or are like most normal human beings and go and chat to people.