In suits such as this, it is a common practice to bring as many possible parties to the table to give the main case more credibility. If EA was the only one sued, then they would seem to be targeted as the only ones that had any potential benefits from the misuse of the representation, which is clearly not the case, even if Nintendo and Sony were not directly involved in the misuse of the licensing.
It would not surprise me if the cases against Sony and Nintendo were dropped, but now it will be crystal clear that if EA is found to be at fault in the misuse of the client's image, they are responsible for a piece of any money generated by it to any company, and that must be taken into consideration. In fact, I would be surprised if Nintendo and Sony did not have legal agreements protecting them from the misuse of licensing by their third party publishers/developers.
To be clear, Nintendo could be held liable if it made money off of a licensed game created by a third party that misuses an owned image, or a person's likeness in the case of an athlete. Even if they did have an agreement with said third party, if they were found to have knowledge of the event (unlikely in this case) they could still be held liable as well.