#3 Their legal issues are putting a glass ceiling over them
The Usos haven’t entirely kept their noses clean during their WWE tenure. First Jimmy faced DUI and related charges; more recently, Jey suffered an arrest of his own for similar reasons. Things intensified when Jimmy was arrested after reportedly standing up to a police officer who had pulled over his wife, Naomi, for which he suffered charges of disorderly conduct and obstruction of justice.
Particularly in today’s family friendly WWE environment, the company places an emphasis on its workers being good role models. As face characters, there is arguably even greater responsibility on the Usos' shoulders, not to mention that they’re now locker room veterans who probably ought to know better than to get into trouble.
As such, there’s the real possibility that WWE is going to hold back on pushing the Usos for a while. They’d like better their prospects of winning tag titles and getting featured in storylines with a move to AEW.