Maybe because the Magicsystem as it is now ingame is not defined.
This update hopefully fixes and sorts the differences in the many spellcaster classes in the EA Version of Game.
Its not normal that Wizard can cast anything even outside of his proficiency like some Clericspells.

Also technically the Sorcerer is less demanding in programming then f.e. Bard or Paladin Class.
Its just the practical decision to bring in the Sorcerer first into the EA after the Basic Characters and classes where implemented to get the EA rollin.
Sorcerer class is less time demanding development of class.

Hope this can give you some insight of how thoughtprocesses in game development is made visible.