Rajamouli and Vinayak are the only directors who were invited to the event by Prabhas. Both Vinayak and Prabhas are good friends for a long time. Even though Vinayak gave him a flop with Yogi, Prabhas never broke that relationship. That is the reason why he invited Vinayak to the event, even though the latter has lost all the fame by scoring successive flops.
Probably no other star hero would do that. Meanwhile, we also hear some other versions on Vinayak's arrival. Apparently, the director is planning to do a film with Prabhas after the latter wraps up Jaan. Meanwhile, Vinayak will also complete the works of his acting-debut film. So, if everything falls in place, we might get a project in this combo very soon.