I have an idea. Maybe the fairies are taking the dust because they are somehow giving magic to the Evil Queen, but they decide to go work for Snow and not giving magic to the Evil Queen. Remember in Ep 2 when Regina says she is losing power they already don’t respect me or something like that. I have always thought she was just talking about losing her kingdom, but maybe she is somehow losing power because she is no longer getting magic from the fairies. I don’t know if i like that idea, but i am putting it out there.