vulnerability : 209 questions
vulnerabilities : 43 questions and no tag wiki
Merge hammer?
It looks like people are using "vulnerabilities" interchangeably with "vulnerability" eg. here, here, and here.
Another common usage would be as a synonym for "vulnerability management" as in here, here, or here. This appears along side "known vulnerabilities" for this variant.
I think the discussion for "vulnerability management" and "vulnerability" go hand in hand, as you do one of two things with a vulnerability -- you fix it, or you abuse it. It would be good if the tag wiki for vulnerability was created with this guidance in mind to assist people in the future with tagging.