Was Management Studio removed from SQL Server 2016 installation media? I just tried installing SQL Server 2016 Enterprise but I noticed that Management Studio was not installed by default. I also noticed there is a separate link to SSMS in the installation guide which points to https://msdn.microsoft.com/en-us/library/mt238290.aspx

What was the reason for this decision? 

The following is noted on the above URL:


  This generally available release of SSMS is free and does not require a SQL Server license to install and use.


Perhaps, this is it?
SQL Server Management Studio is now available on its own page:
SQL Server Management Studio - Release Notes 


  Welcome to our generally-available release of SQL Server Management Studio! This release of SQL Server Management Studio (SSMS) is a stand-alone install outside of the SQL Server release. Our goal is to update this frequently with new functionality, fixes, and support for the newest features in SQL Server and Azure SQL Database [...]   
  
  
  Download SQL Server Management Studio 
  Previous SQL Server Management Studio Releases
  

It is free and no SQL Server licence is required anymore:


  This generally available release of SSMS is free and does not require a SQL Server license to install and use.

It is now updated on a monthly basis since June 2016: Announcing SQL Server Management Studio – July 2016 Release