As I understand it, the only reason Guinan left an echo behind is because she was "pulled...ripped away" by the Enterprise's transporter beam. So it's not like everybody who enters the Nexus leaves an echo, only Guinan and others like her.
So Picard and Kirk did not leave echos, because they left the Nexus voluntarily.
So Picard and Kirk did not leave echos, because they left the Nexus voluntarily.