I don't know of anything here that requires a social media account.
CrowdFlower requires a facebook account. At facebook, you can
have multiple accounts. You don't need to socialize.
However, you may notice with many sites and programs, a Facebook
account is required also. Even big company sites.
I suspect it serves several purposes. For example much easier to
log in and sign up, ip track to prevent cheating, etc. Oh and password
recovery can be much easier.