Exchange Not Working if recovery data Center Shutdown

here is Scenario:

2 Mailbox servers in Primary Data Center 

2 Mailbox Servers in Recovery Data Center

With one DAG Across Sites, DAG has IP 2 Addresses (One for Each DC Sub-nets).

Witness server: Primary DC Server ( Primary data center)

Alternate Witness: Secondary DC Server (Recovery data Center)

Cluster: Node and File Share Majority

DatacenterActivationMode: DAGonly

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Issue:

if i shutdown recovery Data center :

Not able to access Email even the Primary Data center was up and Exchange Server was running fine, I Check the Mailbox Databases and It has shown the Database "Dismounted" on Primary Data center Exchange Server with Activation Pref =1

I check the Cluster and Cluster Was Down.

As FSW was Up and Accessible, and Two Nodes in Primary Site were UP then Why It happend?

Screen Shots are Attached.