C469 Permian
The reason the old expert agreed to help Huo Dongshan was due to Little Granddaughter and Niu Niu's injuries. Now that Niu had fully recovered, the old expert no longer had anything to worry about.
Even if Su Yang asked the old expert to stay, the old expert would not hesitate at all. In the old expert's eyes, it was an honor to serve Su Yang and it could also be considered as repaying the favor