Why was the pronoun tag removed?
Let me quote the Help Center:
When should I create new tags?
Most common tags already exist on a mature site. You should always favor existing tags; only create new tags when you feel you can make a strong case that your question does cover a new topic that nobody else has asked about before on this site.
The existing tag that covers the topic of these questions is code-of-conduct. This isn't the first time that pronouns are the subject of discussion on Meta Stack Exchange:
(from searching for 'pronouns')
Lastly, while if you're even a little bit aware of the current events, it's crystal clear what we're talking about when we use the word 'pronouns'. But in a few years, it may be less so, especially for new users. They could equally well think 'hey, pronouns are on-topic here, let me ask an English grammar question about them'. This question is also about pronouns, but not in the way we're currently talking about them. A more specific tag (maybe [code-of-conduct-pronouns] as suggested by Ruben) might have more merit, but I think the volume is simply too low right now and hopefully it won't grow too much in the future.
Maybe a tag disappears once it is no longer associated with any questions.
You're right: tags are automatically deleted (after ~24 hours) if they have no questions, or (after six months) if they have only one question and no tag wiki or tag excerpt.
(but I hadn't read his response because he forgot to ping me).
I'm sorry about that, I assumed that since you posted the last comment it would automatically ping you. It turns out it doesn't, so I've added this exception to the proposed FAQ.