It's not that Clockwork doesn't fit.Yeah I dont get the issue with the Sorcerer thematically, nor the issue with Clockwork.
They are all different in how they access magic.
It's that Clockwork Sorcery isn't iconic enough to take a spot over more iconic Sorcerer types. FavoredSoul/Divine Sorcery, Storm Sorcery, and Shadow Sorcery are more iconic or have more history. Even sorceries that aren't in 5e like Cosmic Sorcery or Arcana Sorcery are more iconic.