I believe there is a chance Shayne is only at Smosh because he knows if he leave Smosh is over, he might feel obligated to stay, or he is just scared of leaving and not finding anything else
It honestly could be a combination of that as well as contracts. Damien is making big steps in his voice acting and it feels like he leveled up, he is now being invited to conventions for his voice work not smosh. If that continues it will be dificult for him to stay at smosh beyond his contracted time.
Shayne is a bit on a similar trajectory because he is a regular guest on the goldbergs. If he had the time and the right role come through he wouldn't need smosh as much but smosh might need him.
the company also hired about four new on screen talent, so the need to keep the established members will also diminish the more the new people settle in.