The four kings were already killed by Ryder with various schemes, most of which belonged to getting close to them.
With the count of the King he had killed in the FBI headquarters, there were a total of Five Kings who were out of the equation, leaving only the seven of them alive.
Ryder again sent Gander to bring the next King to what was going to be his graveyard. Now that the process was in full swing, things progressed smoothly. And with an insider helping him in this job, things were even faster.
Gander kept bringing Kings to Ryder, who kept killing them one after another. At one point, he even felt like things were too easy.
The Kings were very arrogant and confident of their strength. They didn't feel like they had any risk. There was only one person who had managed to harm even one of them in their eyes, and that person was on a vacation, so their defenses were even more non-existent.