VoWiFi: Why the ePDG is designed to be behind the PGW?

CORE
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17

It might not.
Let the ePDG support WiFi and AAA with HSS.
I am not denying that.
Why they complicated ePDG to have GTP to talk to PGW?
If they would have bypassed PGW, then it would be a thinner protocol stack for the ePDG na… like the below:

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