#3 Past issues with the Shield's enemies

When Roman Reigns was dealing with leukemia, Braun Strowman was resisting like a lone warrior against Drew McIntyre, Bobby Lashley and Baron Corbin. Though he had the help of Finn Balor and Elias, Strowman seemed to clash with them all alone. All the three heels destroyed Braun multiple times. They even put him on the shelf with an injured arm.
Thus, Braun Strowman has a logical reason to join forces with Roman Reigns and Seth Rollins. The possibility that the Shield vs the Dogs of War 2.0 feud will continue even after WrestleMania 35 is high because of the matches that WWE has advertised for the pay-per-views after WrestleMania.
Cody Rhodes' uncle is a WWE Hall of Famer. More details HERE.
WWE can portray Strowman as an honorary Shield member in this storyline by having him join the faces as an equalizer.