It is because of 2 per day short rest restriction - once they rework rest system(hopefully), it will become more balanced. + i think we miss out the strongest warlock sub class - hexblade
I'm not aware of any claim that they intend to rework the rest system, frankly.
But back to the topic...
I don't think the class is particularly ineffective (Eldrich Blast is probably as powerful as a cantrip can ever hope to be and some occasional extra utility in the form of extra spells can help, not to mention that as a charisma-based class the warlock is implicitly a good fit as the "face" of the party.
I do concede that it may not be a particularly interesting or fun class to use, on the other hand. But then again, not many are at level 4.
