Why Didn't apollo creed fight clubber lang?

I've always wondered that. Back when the movie first came out I accepted the idea Ok Apollo retired and maybe his best days were behind him but lo & behold he was more than willing to come out of retirement (even though it was an exhibition match) and fight Drago. Just saying Apollo was till obviously in good shape and it would've been a great way to end his career having come back and regained the title. He only had that one loss to rocky in his career. Plus Clubber was calling him out and disrespected him before & after the 1st fight with rocky. I know , I know it's a movie and the movie is called "Rocky" so Duh of course Rocky would get the fight but from a character standpoint, that's always a question I had. Why was Apollo so hell bent on helping rocky get his "eye of the tiger" back and regaining the title as opposed to doing it himself. He obviously felt he had the formula to beat clubber and he had a score to settle with him.