<p>There are multiple good reasons mentioned in the comments, but let me add my five cents, especially as you <a href="https://stats.meta.stackexchange.com/questions/4384/is-dirac-delta-worth-its-own-tag/4417?noredirect=1#comment11493_4417">pinged me</a> on my own question</p>

<blockquote>
  <p>So, we promote the identity function for convolution to tag status,
  but not the identity meta.stats.stackexchange.com/questions/4440/….
  So, we name individual leaves, and ignore their tree. What, I muse,
  would we do with a whole forest? LOL.</p>
</blockquote>

<p>I guess that you mention <em>the</em> reason why your proposal was downvoted. Such tag would be <em>too broad</em> to be helpful. Using your own example, <code>[forest]</code> tag is not helpful if you are looking precisely for <code>[blueberries]</code>, or <code>[mushrooms]</code>, and if you are looking for mushrooms in the forest, then since they are a subset of items in the forest, it is enough to search for them directly. I guess that if you are looking for information involving identity, then you are not interested in going through all the possible identities in probability theory, but an identity that is connected to some specific problem of your interest.</p>

<p>Moreover if we had <code>[identity]</code> tag, then maybe we also should create other tags as: <code>[equality]</code>, <code>[ineqality]</code>, <code>[integral]</code>, <code>[axiom]</code> etc. What if you asked a question that involved using some axioms, identities, inequalities and calculating integrals? Would using all those tags be <em>really</em> needed in here? How would you decide which of those tags are more important then others?</p>

<p>You could check also <a href="https://stats.meta.stackexchange.com/questions/3031/tag-candidates-for-removal#">Tag-candidates for removal</a> thread or go through <a href="https://stats.meta.stackexchange.com/questions/tagged/tags">other discussions about tags</a> to see why we deleted or considered deleting other tags. In general, <em>too specific</em>, or <em>too broad</em> tags are often considered not very useful.</p>
