#1. To fully establish Roman Reigns as a heel
Roman Reigns has been and will be the guy of WWE. With John Cena long gone and only appearing occasionally, Roman Reigns has been the biggest full-time Superstar that WWE has by far.
WWE and Vince McMahon spent years trying to actively push Roman Reigns as John Cena's successor to the point where they tried to make him just like John Cena - but that didn't work.
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With WWE now in the COVID-era and things having changed quite a bit, it appears that the hesitation to turn Roman Reigns heel is finally gone. However, WWE still hasn't fully established Roman Reigns as a heel. It would be easy for him to simply beat down a babyface, but they needed to be careful about which babyface it was.
Jey Uso makes a lot of sense in that role since he's a family member of Roman Reigns and it plays in well to his storyline and character development. Jey Uso might be a sacrificial lamb to establish Roman Reigns as WWE's biggest heel today.