A preponderance of the following reasons, all of which I make no judgement on, is enough to keep them separate:
- a reasonable user might find one tag interesting but not the other
- there are sufficient open questions or the potential for such to keep the distinction
- merging would significantly impair searching (NB: consider the fact that all of the articles are stop words in search)
This isn't a particularly urgent issue, but any discussion would be welcome. If you have sufficient reputation, you can vote on the tag synonyms yourself.