It was no secret among them that they had this idea as part of the counterattack offensive. It's just that after talking with Kraft and the others as Jin caught up with them, the Dungeon Supplier had decided to change his targets.
After killing that many Mechanoids within the compartment, the System already had the data needed to not just launch a counterattack against the temporary base that was built right outside Mount Sunn but a target that could once and for all put this matter to rest.
Hitting Diamondz main headquarters.
By doing so, they would not only suffer losses but also have the chance of hitting their main CEO. (Although Diaz was saying it would be hilarious that they strike the main headquarters and the CEO is having a vacation.)