Private and more secure sites on the web vs. Public and less secure sites on the web is the real issue.
People with disabilities embraced online communication before social media sites came into the picture. Many PWDs continue to stay strong with those communities and do not feel social media sites have embraced the PWD online social scene.
Studies have demonstrated that PWDs are more online than the general public and might not be using social media but are using the web. I guess the question is how can social media attract PWDs to their websites?
The web is unsafe but you can join a moderated, private and/or secure site to socialize. Many PWDs and/or caretakers because of safety prefer secure or private sites for socializing.
It might not be just an accessibility issue but the way social media sites are run? The conversation style between PWDs and PWDs is vastly different than that between PWDs and non-PWDs. PWD conversations might leave them open to bullying on social media sites.
Bullying is on the rise on social media sites and PWDs are different making them more vulnerable to bullying.