OK, so when did the Scrum-of-Scrums become a meeting of the ScrumMasters from each team in a multi-team environment? Maybe I missed something, but let me state what the original intent of the Scrum-of-Scrums was about. Since Scrum is all about self-management and self-organization, the idea was to let teams work out their coordination, dependencies, and obstacles. The intent was to have a representative team member (specifically not the ScrumMaster) from each team have another daily Scrum of 15 minutes to ensure coordination between teams. The ScrumMasters often rotated to act as ScrumMaster for the Scrum-of-Scrums. This was a fast, easy, efficient means of keeping teams synchronized on a large system development. This teaches the team members to take responsibility for coordinating with each other.
Now, there is nothing wrong with ScrumMasters getting together to discuss obstacles, process related topics, and new tools/techniques for improving. The early large implementations of Scrum mostly referred to these as the ScrumMaster community. I strongly encourage that approach to shared learning for any group of people in a specific discipline.
I believe that this trend is nothing more than a form of control from people in ScrumMaster roles that used to be project managers. Information power...having info that others don't, is a form of control. It's time to let go folks! It's OK, nothing will happen, everyone will be fine. Smart working adults will learn to coordinate their activities just fine. My suggestion is to get focused on the obstacles that nobody wants to deal with or find ways to improve the process or the development environment.