They are finding the most effective duo at the C and RG spots. Is Allen/Corbett better than Corbett/Evans? That's the question.
I have to disagree with the take some have that this is some error in judgement the Rams have made about Corbett's ability to play center. They are simply reacting to what their eyes are showing them right now which is Allen solidly asserting himself. This isn't over yet. Obviously Corbett is a more natural and better guard than center. And if Allen is proving capable then that's the duo that makes the most sense.
It's August 12th. I would say this is not set in stone until around the 25th-26th. Allen's main issue in 2019 was lack of size and strength. He's seemingly addressed that the past 18+ months and if he can hold up in the middle then great. And then ultimately they'd be returning 4 of 5 starters in the exact same spots as 2020.
As someone else posted, maybe- just maybe- they've simply got lucky.