Why don't Athiests, Muslims, and any other people who don't believe in the Trinity give in?

I quote John P. Kee "How much longer do you have to go through before you realize/That theres Someone greater than you but you still deny?/ He died up on the cross just to save the lost/and forgave us for our sins, so we may live again/His love is unconditional/He'll be there for you don't you know/I'll tell it everywhere i go yeah yeah"