It's marketing, you do whatever you have to do to sell your product. It's a completely separate department from the developers. You can read into it all you want, but it has nothing to do with the people actually making the game.
P.S. I'm going to go out on a limb here and say that the Bioware developers know exactly what the issues are. The problem is they have only a few limited options to fix it. They can't rewind time and re-release the game; a lot of that joy and surprise that should come from the ending is just lost. Even if they went back and put in some foreshadowing elements in earlier parts of the game about Starkid, some people will always regard it as coming out of left field. So, they're doing what they can do: expand and explain the ending we were given. Give a sense of closure, give the players an idea of what the future of the Mass Effect universe holds.