> reduce operating expenses

If you assume they are immune to politics (not true but let's go with it), this is the most obvious reason.

They've seen X hasn't taken that much heat for Community Notes and they're like "wow we can cut a line item".

The real problem is, Facebook is not X. 90% of the content on Facebook is not public.

You can't Fact Check or Community Note the private groups sharing blatantly false content, until it spills out via a re-share.

So Facebook will remain a breeding ground of conspiracy, pushed there by the echo chamber and Nazi-bar effects.