Apparently, universes are destroyed only when 1) sometimes when the use of a universal nullifier interferes with the universe's big bang, causing the universe's premature death and 2) universes that have Earths collide with each other and both are destroyed.
When an Earth is destroyed during an incursion, NEITHER universes are destroyed. In addition, universes that no longer have Earths no longer suffer incursions and can't be destroyed during them, BUT will still be destroyed when the multiverse itself dies.
So Black Swan is accelerating incursions but by destroying the Earths she is saving the universes. So Rabum Alal wants the multiverse to still exist but either wants all Earths removed or only one Earth to remain. Or perhaps the goal is to get rid of heroes who are not willing to destroy other Earths to save their own universe, or to get rid of a specific Earther. It's all speculation.