To observe, is to ask questions: What is happening here? How did this come to be? Is there a pattern to this? What existing pattern does this align with? Observation is fuelled by curiosity. We observe with our awareness. To observe is to understand things as they are.
To judge, is to also ask questions, but different ones. Is this good enough? Is this beneficial? Is this better? Is there some progress? The central idea is comparison among different things or to a standard. To judge is to interpret things in relation to how we want them or expect them to be.
We are born with the tendency to observe and be curious. This innate quality morphs into judgement with time. The spiritual quest pertains to going back from judgement to observation.
Because curiosity is central to who we are, while judgement is the illusion that is caused by our conditioning.