Why did they not choose Tommy instead as the fake Jason

Still have Roy as the suspected killer because of his son being killed, but it would had made more sense to have Tommy as the mystery killer instead of Roy...Tommy does have psychotic issued throughout the film to begin with...Why does he killed only at the end?just because Jason re-appears again...Doesn't make sense, he appeared several times before...

The ending would had made more sense, Tommy is at the hospital from falling off onto spikes & severe cut injuries - He gets rejuvenated by the apparition of Jason & he puts on the mask on & waits for Pam...

Who else knows better Jason than Tommy since he is the only one to have seen him in person before killing him & he knew what Jason looked like physically & his style of killing ...