What are the reasons why Database Mirroring cannot be used for system databases?

I just want to know the reasons why Database Mirroring cannot be used for system databases.

A mirrored database is not available for access , since it is in "recovering" state which implies that system databases can not be mirrored and is not intended as the replacement for replication).
You can, however, get around this limitation by creating a database snapshot of the mirror and use it instead. It is also not possible to create separate mirrors of the same database.
http://www.databasejournal.com/feat...ability-Enhancements---Database-Mirroring.htm
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