They have commented on it earlier in SL. The main thing is they don’t want to destroy the meta in the middle of it. So people don’t regret the choices they made on which classes to focus on if it suddenly gets nerfed mid-progression and such. Don’t want to shake up the boat with every wave.
They prefer waiting for new tier seasons for the major balancing changes because it’s a reset on gear and progress, a good time to mix things up in a more dramatic way. In between patches it’s usually lighter tuning or on the really game breaking outliers. But that’s the gist. It’s not out of laziness, it’s being intentionally cautious.
Not my opinion, I’m just the messenger. 