In short, it’s really hard to extract. The issue is the stability of CBDa. Imagine CBDa is like an ice cube. When it’s exposed to warm temperatures it melts very quickly, what makes us different is our ability to stop the ice cube (CBDa) from melting (decaying).
All CBD comes from CBDa but because it’s so unstable it reverts to CBD which is why it is a more common ingredient in products you see today, not because it’s better but because it’s easier to make!