Why can members of db_datareader SELECT sys views

In SQL Azure my understanding of db_datareader is that it is allowed to SELECT all user tables.

I couldn’t find a definition of exactly what a user table is, but I assumed it was all of the non-builtin tables and views, and excluded all the views and tables that are in the sys schema.

Why then can members run the following statements?

SELECT TOP (5) * FROM [sys].tables  SELECT TOP (5) * FROM [sys].[all_views];  SELECT * FROM sys.dm_exec_sessions;  SELECT TOP (5) * FROM [sys].objects 

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