Originally Posted by Nell2ThaIzzay
Because Jean is more marketable than Mariko. Audiences know Jean. They don't know Mariko.
I bet we saw in the trailers all there is to see of Jean in the movie.
Also, I would imagine that since audiences unfamiliar with the comics wouldn't know who Mariko was anyway, and the lack of decent action sequences in the first film...they want the trailers emphasize more of the combat and less of the Wolverine-gets-a-girlfriend aspect.