Well Stew, I'm guessin' selling the concept of a sequel, an already known entity and proven money-maker in the past, is always going to be an easier sell to Hollywood producers than an idea which has no track-record. And those dudes certainly know how to make the moola...if not necessarily "art".
And thus...Sly Stallone in "RAMBO 5: Steroids Of Menace".(...or whatever the subtitle becomes)