Why does the count not match Facebook or X?

It is not meant to. We count presses on your buttons, on your site. The networks no longer publish share counts for anyone to read: X and LinkedIn took theirs away, and Facebook gives one only to an app that asks with its own access token, with likes and comments counted in.

Your number is the more useful one anyway: it tells you which buttons your readers use, which is what you would change something about.