It is called SignWriting for all you multiple naysayers.
I suspect Meta/Facebook doesn't have a lot of content to work off of. I've only been able to find community-generated examples of SignWriting on the official website[1], and none of those seem to be using Unicode characters. MMS is an audio-to-text tool, so it seems unlikely that it can be trivially expanded to take in visual data (pictures of text or video of ASL being performed).
I suspect the process of turning viewed ASL into SignWriting text will be very difficult to automate. I would not be surprised if such a project would either use a different textual encoding or directly translate out to English (which also sounds terribly hard, but these LLM advances recently have surprised me).
Looking into it, it seems very much at the experimental stage in terms of digital representation -- while Unicode symbols exist, they require being placed in 2D boxes (using a drawing tool like SVG). It seems like it's only in the past few years that there have been proposals for how to turn it into a linear canonical text encoding?
Is anyone actually using those linear encodings -- SignPuddle or Formal SignWriting, they seem to be called -- in the wild, outside of demonstration texts or academia? Especially since they only date to 2016 and 2019.
Is there anywhere close at all to a corpus that Meta could train on? Because it still seems like the answer is no, but I also got my research wrong when Google gave no indication that SignWriting existed in the first place.
Which is that I can't find any indication of a linear digital encoding that has been used to any appreciable extent that Meta could train on a corpus of it.
Which is why I'm struggling to understand why you're criticizing Meta? How could they realistically train a linear text model on ASL when the necessary content doesn't appear to exist?
Instead, go by hard-of-hearing, people with hearing loss or simply, Deaf.
Also "deaf" is barely ok when use alone for the above generalized replacement however "deaf" often poorly is refers to most severe of hearing-loss as determined by differing standards of hearing loss, but capitalized "D"eaf is a direct reference to those of actively using sign language and engage within deaf culture, whether it would be American Sign Language, British Sign Language, or some 40-odd variants and different nationalities.