We don't need it.
I will agree with what was stated in the answers of the Worth of "GM" and "players" tags question.
My opinion on tags is simple: if I go into the tag query, I should know what I will be looking at. IMO tags are mostly used for filtering and searching. If I have a metagaming problem and I want to check if it was already asked, I will search the metagaming tag. If I feel I have decent lawyering skills, I will put the rules-as-written in my favorites and look for answering these. Point being: the tags I personally consider useful are tags that describe what the question is about.
The players tag doesn't. As you said, if I look through this tag, I don't know if I'm looking at "I am a player" questions (which doesn't actually need a tag, imo), "I have a problem with a player" questions (which can be either my problem with him being as a player or as a person, so either problem-players or something social or group-dynamics as you said) or even simply "There are players involved" (which any question about an actual table will have, supposedly). Point being: I don't have a clue what I would be looking at if I went through the players tag. (tbh I didn't even know it existed until now). Many of the questions are actually gm-techniques questions, and I wouldn't expect that in a tag called "players".
Okay but how do we know that's not just you being dumb?
Well, I searched through the tag. I still don't know what the tag is about.
- How can I interest a player in playing online? - this is simply online-roleplaying and possibly a system (in this case, tagged as agnostic, but I do think the system makes a difference here.)
- How can I, as a player, help a struggling GM at a one-time game? - this is a question that I can't think of a good describing tag, but it's also not a question I would
- Keeping the world alive whilst PCs take a rest mid-adventure? - the players tag doesn't tell me anything (actually it's more like a gm-techniques than anything actually related to players), the LMoP, dnd-5e and rests do. They are enough. I actually took the liberty to edit out the players tag and add the gm-techniques. :P
- How to extract yuan-ti poison? - "There is a player involved and he wants to try something, are there rules for it?", really, we don't need a tag for the "there is a player involved and he wants to try something" part. The tags just need to tell what is "it" (monsters, poison) and where should we look for these rules (i.e. the system, dnd-5e), imo.
- How to deal with a player missing the first session of a campaign - this is the only case where players was the only tag in the question. We have the absent-players for it, though, which actually describes something (that we are dealing with a problem related to players missing one or more sections). Reason I am saying "was" the only tag - I edited it :P
I'm not going to paste and justify all the questions, but I have at least read the title of most of the 123 questions and I didn't see a case where the tag was useful.