Google's John Mueller addressed the question of why they don't disclose most Google algorithm updates and changes in this mornings Google hangout not just once, but twice. He did so at the 8 minute mark and the 14:18 minute mark into the video.

The short answer is that Google does hundreds of changes per year and it isn't useful, in their perspective, to disclose that they did two updates today, 3 yesterday, 2 the other day and so on. He said it isn't useful to do so. He added that when Google can give specific guidance to webmasters, like with the mobile friendly update, where they can give webmasters notice to make their sites mobile friendly, that is something actionable and useful.

I should note, Gary Illyes from Google recently said Google doesn't deny algorithm updates. But not denying and confirming them are two different things...

Let me share each video embed and the transcript so you can watch yourself:

(Q) Can you tell me a little bit about this Fred update? Is this an official update or something? (A) It is one of those updates that we make all the time. There is nothing really specific that we would have to communicate about that. (Q) Why are you not disclosing this one? We tend not to disclose most of the updates. We make them like hundreds a year, so for the most part, it doesn’t make sense to say oh, we made a change today, we made a change yesterday, we a change today, we made two changes yesterday.

(Q) When or how does Google decide whether to announce a ranking boost or change? For example, the mobile interstitial, the HTTPS, the mobile-first, etc? (A) So this is something that, from our point of view, is sometimes a bit tricky but sometimes it is kind of obvious as well. In the sense that if there are things that we can clearly tell webmasters what they can do to improve things on their side, then we will try to do that. So for example, when it came to the mobile friendly ranking change, which was two years ago, that is something where we recognized that this was a big problem, a lot of sites were not mobile friendly. We wanted to make changes to search results in that regard. And to make sure sites had a chance to understand what is happening and kind of make that right decision as well we wanted to kind of spread that word and say hey, we are doing this, you can do this on your site to kind of make sure you are in line with this. And in general the recommendations we have on this are not just for search, they are something that are relevant for webmasters and web sites across the board. So the mobile friendly change is something where of course we can take that into account for search but where half of your users are coming from mobile devices, it is something you want to take into account as well and kind of handle on your site too.

Forum discussion at Google+.