After Ainsworth spread his monster virus throughout the entire Monster World, it was a given that most of the monsters had already been assimilated into his Hive Mind.
But this time, he didn't steal the monsters from the Monster World aside from increasing his captured SS-rank Monster Lords to ten, just to make it an even number.
As usual, he didn't want to alert the Monster World's World Will. But aside from that, having more than ten SS-rank Monster Lords wouldn't make much of a difference. After all, he was far stronger than those Monster Lords, and their use was only to be a guardian beast for his teammates in the next Otherworld Mission.
It was worth noting that even though he didn't take more SS-rank Monster Lords, he still captured powerful S-rank monsters that could fly or swim. He planned to make use of them as carriers of his viruses if he ever arrived in the Otherworld, so they were merely disposables.