I thought this was just because you do not yet have the approve tag wiki edits privilege that comes in at a reputation of 5,000.
I also wondered whether there might be a tag wiki edit pending.
When I look at https://gis.stackexchange.com/tags/error-000666/info with moderator privileges I see:
so I could easily create the tag wiki by clicking
Create Tag Info but I would like to investigate a little more first.
Shouldn't there be an explanation for a missing Edit Tag Wiki button? seems to shed a little more light on the history of tag wiki creation/editing functionality but I think fails to explain what you are seeing.
I've asked around in chat rooms and a few other moderators have taken a look but at the moment this seems to be non-reproducible so I don't think we'll be able to do much until it occurs again and remains reproducible.
As discussed in our comments I think we have now nailed the cause as being that you already have 5 suggested edits in the review queue and are being temporarily rate limited (Rate limit suggested edits). This seems confusing so I have posted a feature request to Meta SE of Show banner rather than having Create Tag info button go missing when user has 5 pending suggested edits?