It strikes me that all the empty units are a symptom of the removal of so many rides over the past ten years.
Back in the 2000s, you had a better variety of rides and thus a better variety of queue times, so rather than spending 90 minutes in a queue for one ride, you were more likely to spend say an hour queueing for that ride and then jump in a shorter queue for a smaller ride. That meant that guests were moving around the park more often during the day and so had more opportunities for spending money on a great variety of things.
These days it feels more like a queue by queue slog through your day at the park. If you've just spent 90 minutes in the queue for one ride and know the next ride you want to go on has a 70 minute queue, you are more likely to rush straight to the next queue. This means most visitors are no longer in the frame of mind needed to be browsing retail, sitting down to eat, playing sideshows or sampling something new.
So basically as the ride selection has wound down over the years it has been constantly followed by all the other units around the park. This then leads to a downward spiral because the assumption by the bean counters is that the units aren't popular/can't be profitable rather then recognising that it overall short-term planning of the park at large that is causing the problem.