#2 Giving the fans someone to root for
Let’s count the champions on the roster. Jinder Mahal is a heel, The Miz is a heel, The Usos, The Authors of Pain and Sheasaro are heels, Alexa Bliss is a heel, Neville is a heel, Pete Dunne is a heel, and so is Bobby Roode. With the exception of Brock Lesnar, Naomi, and Asuka, every champion is a heel.
This is why fans have nobody to root for, no strong babyface champions. Having AJ Styles as a US Champion allows the company to have a popular babyface champion be cheered, considering their only other over babyface, is the General Manager of SmackDown.
Compare this to the most memorable eras of WWE, when popular babyfaces such as Hulk Hogan, The Ultimate Warrior, Stone Cold Steve Austin and The Rock held the top prize.