Here's the real answer retard
They want every update to be meaningful and give a massive bang for your buck, especially when the game is so new and they want to ensure longevity of the game
Instantly filling up all design space with overbloated PoE 1 shit mechanics means any new mechanic or league they make is less impactful and relevant
It's the reason 0.3 will be so big, because they actually have space to design interesting things.