Like in the Intelligence world, often times people do not value information that comes too cheaply, nor too easily. Social media delivers information (and noise passing as information, as others have pointed out in this string) and it may be picked up by elements that are interested in listening. But unless that garden is tended to, the weeds/noise can grow unwieldy and kill any fruitful harvest.
It’s important too, to note the differences between a work related social network and a friends and family social network. Each has their place. Engagement fatigue is, in my experience, more related to personal social media elements (“Sheesh you go to Starbucks an awful lot!”) than work related social media forums.