Thanks for bringing this up! I'm surprised that this discussion hasn't already been had.
I'll start by noting that the situation today is far better than it was a year ago: nearly half of the questions tagged [song-title] were also tagged [identify-this-song] until the conflicted tagging was cleaned up; see my earlier Meta question:
Today, that number is far less.
Now, I agree that the [song-title] tag needs some cleanup, but merging it with [identify-this-song] would be too drastic.
It sure looks like most questions tagged song-title are either "What is the title?" or "Why is this song called X", the latter of which can often be resolved by a quick Google search.
Questions like the first kind are, in my opinion, song identification questions in disguise, so they should be retagged as [identify-this-song].
However, questions like the second kind are definitely on-topic for us. One purpose of the sites in the SE network is to become a repository of commonly asked questions within each site's scope, so being easily Google-able is not a problem if the questions are otherwise well-written and on-topic. Moreover, one should not judge the very old questions on this site by the same standards for research that we have today, five years down the line.
I describe below how the questions currently tagged [song-title] are distributed:
4 0 questions are about identifying a song:
3 1 question is completely mistagged:
1 0 questions are about the meaning of the lyrics, not the song title:
15 questions are about the meaning of, or the reason for choosing, specific song titles:
5 questions are about the meaning behind generic phrases occurring in song titles:
2 questions are about the "real" title of a song:
1 question is a list question about song titles:
Even with "only" 23 on-topic questions, this would still make [song-title] on of our more popular tags, sitting at the top of page 2 in the tags list! Rather than merging [song-title] with [identify-this-song] or burninating [song-title], I suggest taking another look at the first 8 questions that I mentioned and seeing if retagging can/should be done (EDIT: this has been done).
It would also be a good idea to flesh out the proper usage of the [song-title] tag in its tag info. Currently, it has an excerpt but no wiki.
Although it is not very relevant in this case, I'll add that some care needs to be taken before burninating a tag because a question can become [untagged] if the the only tag on that question is the burninated one. The list of questions solely tagged with [song-title] can be seen in this SEDE query.