Disclaimer: I don't own Naruto...
The real reason why Kakashi finally passed a genin team.
Because he had to.
Sandaime had told him to take a genin team or his hitai-ate would be taken and his ninja rank disqualified.
Hokage said that he had taken too many S-class missions for it to be healthy. Underneath the underneath, he meant that they were afraid that he might lose it. And Konoha wasn't in the position to lose such a great ninja. Partially Sandaime feared that Kakashi might voluntarily give up his hitai-ate and try to live a normal life after so much death and killing.
As Kakashi later told Sasuke, all precious people in his life were dead. Maybe a little more laid back job would suit him. Teaching couldn't be that bad…
Later Sandaime, if he were alive, would have regretted that decision. It was devastating for Tsunade to witness Kakashi's isolation from others as his genin team slowly fell apart. Kakashi once again lost the precious people in his life. His genin team had begun to heal Kakashi and his torn soul, they had become some sort of a family.
Sasuke left to Orochimaru, Jiraiya took Naruto and Tsunade herself started to teach Sakura.
Once again Kakashi's team was left with him only.
Few years later someone found Kakashi's hitai-ate on the Memorial Stone. Kakashi was found from the waterfall of the Hokages. He had taken his life with the same sword as his father all those years ago.
A month later Sasuke came back after killing Orochimaru and Naruto returned with the more powerful Rasengan. Sakura dismissed herself from Tsunade's apprenticeship and they formed the Team 7 once more.
But it wasn't the same with Yamato in charge. Something was missing.
That something had finally been reunited with the rest of Team Yellow Flash.