That isn't how that works. They chose the roster when the project plan started. They didn't say "Hey, let's make this character an assist to piss of their fans." They actually are more like "Hey, we don't have enough time and resources set aside to make this character, but we really think they have fans/are important to the industry/Nintendo- maybe we can make them an assist because it takes less time and resources to do." It still takes time and effort, but not as much. They got added as an assist because of their fans and importance. Smash Bros will never have a roster containing every character somebody in the world wants, but they try and give nods to the more popular and important characters in many different ways- Assists, Items, Stage elements, etc.