It sounds like you're spot on. Despite the potential micronutrient density, most juiced "shakes" are low in calories, food reward/palatability, etc. though it is possible to do otherwise. At any rate, think about it like this: Say you want to lose weight but you have a habit of falling off the wagon (non compliant) all the time. We reason this out to be a case of having too many options, too many potential rationalizations of binge eating behavior, etc. What sort of diet protocol is likely to work for you at this juncture? One that you don't have to think about and is pretty hard to screw up. Enter the shake-based diets (of all types). How do you know you're doing it right? You're only drinking the shakes (so there's no potential to screw it up without intentionally sabotaging yourself). Similarly, since the food isn't that palatable (the shake), it's pretty hard to overeat so people lose weight.
This is similar to the classical amino acid + vitamin + fish oil diets researchers used on obese people in the 20's and 30's, e.g. use a bland liquid based diet and people are massively calorie restricted and lose weight.
Problem is, without sustained accountability and tracking (e.g. weighing/measuring/logging/etc.) the propensity for weight gain is almost insurmountable. The latest I've seen is >95% tend to regain even more weight. The majority of these 95% are folks who lose a diet in a quick manner (biggest loser for instance) or in ways that don't involve consistent accountability.