The main reason is probably the successful setting of 7 dwarfs with different personalities. Thinking about it further, these seven people also constitute a very interesting community. The doctor is an intelligent leader who rules not through force but through experience. When working in the mine, he was the only one who identified gems without manual labor. Grumpy is the de facto second-in-command. His role can be understood as whip, which regulates the behavior of everyone else through provocation. The rest constitutes the bottom layer in the community, but there is the bottom layer below the bottom layer, the fool who has no beard and can't speak. This role seems to represent the apprentices in the traditional craftsman group, indicating that young = inexperienced = incapable = no right to speak.
As for the princess and queen, according to the current aesthetic standards, Snow White is probably too sweet and greasy, but the queen may be more pleased.
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