Why is cross db ownership chaining on by default for system DB I am reading about cross db ownership chaining Server Configuration Option

It talks about how and why to use (or not) this option and says 


  Setting cross db ownership chaining to 1 is not recommended unless all of the databases hosted by the instance of SQL Server must participate in cross-database ownership chaining and you are aware of the security implications of this setting. 


It also offers this code to check. 

SELECT is_db_chaining_on, name FROM sys.databases;


According to Server Configuration Options (SQL Server) the defualt value for 'cross db ownership chaining' is 0 (zero) 

When I run it on my servers, old, new or whatever they all seem have it enabled on master, tempdb, and msdb.  I checked a few from SQL 2012 to SQL 2017, Enterprise and Standard editions. 

I did find that it where it is set to on by default but not why.


tempdb settings Can not be altered
master settings Can not be altered
msdb settings Can be altered


If it is bad, why is it on by default on system databases? 

Why am I not finding anything talking about why it is on by default on system databases?
I have continued to search for reasoning behind this.  Everything I find is some version of 


  These system databases must have cross-database ownership chaining turned on in order to function properly source


Clearly the system databases; master, tempdb, and msdb are interdependent. Presumably early in SQL development, some microsoft developer made the choice to use cross-database chaining to solve access issues, and it has never been updated. 

Another of of those things that is Microsoft recommends not be used, but they are dependent on it.