On the March 26 episode of SmackDown, Asuka lost her SmackDown Women's Championship in an unannounced match against Charlotte Flair. It was panned by many fans as rushed, unplanned, and unfair to a performer of Asuka's caliber. It also undid WWE's previously announced plans: To hold a Fatal 4-Way for a No. 1 contender and book that winner to fight Asuka at WrestleMania. Now, with Asuka beltless, all these SmackDown women (including Asuka) have been entered into the WrestleMania Women's Battle Royal.
According to Meltzer (h/t Dominic Deangelo of WrestleZone), this decision was actually made the day of the show by McMahon. His motivation was to eliminate a match that he felt most fans would not care about, and to add additional stakes to the Triple Threat women's main event, which was already being contested for the Raw Women's title. Now, it'll be contested for both women's titles in a "Winner Takes All" stipulation.