That is because the tag already has a tag wiki. The [wiki got approved](https://stackoverflow.com/review/suggested-edits/361678) and the [excerpt got rejected](https://stackoverflow.com/review/suggested-edits/361679) when the first user edited it. Tag wikis are only displayed when the tag *also* has an excerpt. If it doesn't have an excerpt but has a wiki, nothing is displayed. If it doesn't have a wiki but has an excerpt, the excerpt is displayed with no tag wiki.

Once an excerpt is added, the wiki will be displayed correctly on the info page.