Convention here (US) I attended Friday only and there was a similar scene with a lot of empty seats. Admittedly, Friday morning is typically the lowest attendance, and it did fill out a bit more in the afternoon.
Based on anecdotes, I think it is clear that the convention planners' formula for how many congregations to assign to a particular facility is falling short. Between the high cost of travel/lodging and the aging JW demographic, it is evident quite a lot are staying at home and (probably) watching the recorded online sessions.
Baptism ratio of # of baptisms / # in attendance is a good measure, as both figures can be verified or estimated by observers, and compared with previous years' conventions. Some of the 1970's' conventions had a ratio in the 2% range; nowadays it is running about 0.5% most of the time.