Question about Rocky 3/4

I was thinking today about Rocky III and Rocky IV, in Rocky IV Rocky vacates the title so he can fight Drago...at the end of Rocky III he says he's retiring after his 2nd bout with Clubber Lang. My question is why didn't Rocky vacate the title after his win? He wasn't going to be defending it against anyone so why did he still have it in Rocky IV? 😕

Maybe having the title was apart of the Russians interest in Rocky. They wanted to beat the World Champion not someone whom was once a world champion. That'd be my guess aside from lazy continuity.

I'd go with the latter