The right side defence has steadied very nicely and they're defending as a unit mostly. To'o is To'o and Tago is playing as well as he has in 2-3 years. He's making ok decisions, ok contact, he's running hard, getting over the advantage line and earning quick play the balls. Those guys aren't getting dropped.
So the left is the only option for Alamoti. My theory is they have adjusted the defensive structure on that side to contract more and protect Talagi a bit knowing everyone on that side has the speed and lateral movement to scramble and cover the sideline. Even Garner has been starting over Sorro the last few weeks. Alamoti doesn't really fit as well into that type of structure.