WotC's rationale behind this change is that Magic: The Gathering is experiencing new growth via digital play, tabletop, and esports, and the flexibility that unscheduled bannings would allow them helps WotC make changes quickly in order not to disrupt the logistics of players' plans to travel to large events. The flexibility will also help players continue to engage with in-store events more consistently without having to wait as long for an unhealthy metagame to correct itself.
As part of a second announcement, WotC also banned Oko, Thief of Crowns and Nexus of Fate in the Pioneer format. This is the second format Oko has been banned in since being released in October, and possibly, not the last (see "WotC Bans Key Cards from 'Throne of Eldraine' in Standard").There have been an unusually high number of banning in various Magic: The Gathering formats over the course of the last year (see "'Magic: The Gathering' Ban Hammer Comes Down On 'Field of the Dead'", "Wizards of the Coast Reveals Latest 'Magic: The Gathering' Pioneer Format Bannings, and also, "Wizards of the Coast Updates 'Magic: The Gathering' Banned and Restricted Lists").