#2 To fill the void left by The Shield
Stables are an essential part of the wrestling business irrespective of the promotion they're employed. NWO was the cause of WCW's rise as well as their downfall when WCW gave too much creative freedom to them.
For a fan who is new to the world of wrestling, who hasn't seen much wrestling outside of US-based promotions, NJPW is synonymous with the Bullet Club.
Similarly, the Shield was the most dominant WWE stable in recent times. Apart from the New Day and the Wyatt Family, no other faction made an impact on the main roster that's even close to the Shield.
With Ambrose leaving the company and the New Day on SmackDown, there's no credible stable left on RAW. The Club could fill that void, and with AJ Styles as the leader, it could become the dominant stable that RAW needs at the moment.