I wouldn't know based on very little information. Many things could be in play. The recurring theme here is Apple the Watch is defective somehow.
Let's assume for your situation your Watch and software are working properly. Your data entered in the Health app is used in measuring your workouts. Given that, Apple may posit an easy workout for you is difficult for me, based on my Health data. Your goals set in any given workout compared to how you complete them will also affect workouts.
In the link I posted previously, you can see that you can close a Move ring outside of a workout or without a specific workout at all. Stands are a little more than just standing, though. There needs to be some movement for about a minute to get Stand credit.
The Watch records all your activity using the common metrics most fitness devices use— average speed, distance, time, steps, temperature, average heart rate, and peak heart rate, I believe. All these are recorded for you to review.
Apple is clearly trying to make us healthier and is focusing on cardio-vascular activity to do so. Closing Move and Stand ring shouldn't be difficult once it's understood what's required. You seem to have no difficulty with closing not only those, but the Exercise ring as well. You might consider increasing your goal(s) and challenging yourself more.
My workouts for the Watch are solely Outdoor Walks. I've found that over three months, it's become a little more difficult to earn Exercise points. At the very beginning I attributed this to slowing down at various times even though my average speed was 20min/mi. When I slow, Exercise credit isn't given. So I made sure I kept my pace up and all was well for over two months. Then I found I wasn't getting minute-for-minute credit. Reviewing my Workout stats I saw that my average heart rate had dropped noticeably from my first workouts. I believe heart rate is one of the metrics used in calculating progress. My improved conditioning made it harder to close that ring, so now I have to push myself a little more.
If you use the Other method, your green ring will close pretty much no matter what you do or don't do. If you have no trouble meeting your current goals within a specific Workout, your green ring will close fairly easily. The other two are fairly easily closed, the red ring also based on whatever goal you set.
Apple has monthly challenges that are based on your data and previous performance to challenge you to increase your level of activity. These will change as your level of conditioning changes.
Check out the information at the above link and consider increasing your goals. That should help you figure out what's what.