About theatrical releases:
With projects like that (the ones that go to theatres), you have big investors. People with real money, who believe in the production. In such, almost always, you don't see Steven Seagal as the producer ... so during film making, Seagal's part is only as an actor and perhaps as a little stunt co-ordinator or choreographer ... but that's it ... if the movie has a big budget, Steven Seagal will most likely have little to say to the exec. producers or to the director so that big changes are made to the film. Therefore, if he's told to come back and do a good voice over for some reason, he will have to do that, or his paycheck will be on the line as well as further contracts with the production team. For such big projects, scheduling is very important, and rushing is never good.
By the way, word of a mouth does not work for Steven Seagal's films, as his name is not as popular nowadays as it was or compared to other big shot action stars; ... and DMX did help with advertising for Exit Wounds but overall "Exit Wounds" wasn't marketed as much as films you see today and it still did amazing at the box-office. That just goes to tell you that people can recognize quality without anybody else telling them about it. (Half Past Dead wasn't nearly as good as Exit Wounds)