I wonder if it's because they don't see other relevant low-cost/overhead solutions. "Follow me on facebook" certainly isn't going to be a win. "Follow me on Bluesky or Mastadon" is going to be ignored. "You can see my comments on insta" won't be relevant. "My TikTok is where it's at" might get you some young followers.

Other solutions (your own blog, medium, substack, etc), all come with more overhead and setup.