We live in a age of instant gratification. Most people just don't have the patience or intention span to deal with long form mysteries in comics. It's weird, because Spencer was been writing the book for close to 3 years. So the wait is nowhere near the one people had to endure when the Hobgoblin one was unfolding.
In saying that, some mysteries do have a lifespan and dragging them out long past their used by date only hampers it in the long run. Look at the Clone Saga 2 where unnecessary twists and turns were added to pad it out.
Generally, I don't mind the slow burn. But I do see, and understand, why some don't.