Linking to something written by your wife without saying that's what you're doing pattern-matches to the following more general template: recommending something being offered by a close associate, without declaring that association. And this makes people twitchy because it resembles two other things that do. First: encouraging people to do something that benefits you or your associates, without declaring your own interest. It should be obvious why that makes people twitchy: you're saying "do X, you'll like it" when you have another reason for wanting people to do X. Second: recommending something that you have specific personal reasons for liking, without mentioning those reasons. It should be obvious why that makes people twitchy, too: you're suggesting that other people will like X, but perhaps you only like it for your own personal reasons.

Now, perhaps in fact you think your wife's article is interesting for reasons that have absolutely nothing to do with her being your wife, and perhaps neither she nor you stands to gain in any way from directing people's attention to the article (though in fact the article just happens to speak highly of you, recommend Intentional Insights, etc., etc.). But as a general rule recommending things in which you have any sort of personal interest, without declaring that interest, is going to strike some people as dishonest, or at least a little bit sketchy.

The point is not so much that it's helpful information but that the social signal that get's send by witholding that information. Including the information sends a signal of cooperation, witholding sends a signal of defecting.

In general it's useful to frequently do things in writing that appear like signals of cooperation or otherwise your writing will feel like it's manipulative even if you don't really intend to manipulate.