The theory is: "There are no defined criteria, but galleries with good technical or artistic quality will float to the top."
I don't see this happening. Rather, the popular galleries seem to be dominated by "special interest" galleries where the subject (e.g. my basement remodelling job, my staff Christmas party), and not the technical quality or aesthetics of the photos, is of interest. Perhaps there are too many slots for popular galleries. Maybe the voting rules could be changed somehow. Sorry I don't have a solution to propose.
I would hope to look to the Popular Galleries for technically excellent and aesthetically inspiring photographs but that's not what I see. Do any others feel this way or is everyone happy with what gets called popular and how the voting works?