> AFAIK he intentionally leaves them out, I don't get why.
Some people like to brag about the timelessness of their articles [1], and that might be one reason. (I personally don't fully agree though, even the linked original WikiWikiWeb page has a last edited date.)
Also wish his pages had dates on them (one or both of first posted / last updated) AFAIK he intentionally leaves them out, I don't get why.