I agree with you that as a reader, often a publication date would be useful information. However, from the point of view of the publisher, it's often better to

I agree with you that as a reader, often a publication date would be useful information. However, from the point of view of the publisher, it's often better to publish 'evergreen' content, that is always maximally valuable to visitors, and to the publisher (advertising, personal branding, authority-building, etc). So if you're trying to do anything like that, it may be best to leave off dates. And as Patrick says, the advice in this post would have been useful 5 years ago, and will probably be useful 10-20 years hence. If you're going for evergreen content, you can write in such a way too. I believe Isaac Asimov mentioned this one time. I think he had mentioned an athlete's name in a story, and said that he regretted it, because in a few years no one would remember the athlete, but otherwise his story would still be relevant.