Deletion on many online services is “soft”. Which is, exactly as you say, just hiding it and preventing it from contributing to various counts/statistics.

I imagine it’s named like that because “hide” implies “hide from myself only” (like hiding a dialog box), whereas delete implies something more permanent.
Also, when a user wants to get rid of something the first word they’ll look for tends to be “delete”, so why make it harder for them to find that button by naming it something unconventional like “hide from all”? Even if it’s technically more accurate, users just don’t care.

I also imagine some services keep some things for legal reasons, even after “deletion”.