Could it be that, for once, the blame lies with the fanbase and not with the art(ists)?
Hear me out
While the original series' are done, they have spawned successors (although their worthiness can be questioned) which carry much in common with the originals. So even if they're not 100% the same, they should have enough to combine with loyalty/nostalgia and keep the numbers at similar levels to past days.
Assuming that to be true, the problem with numbers dropping should then lie with the fanbases.
How so?
It could be that a feeling of seniorship has taken grip of fans of the original series and they unfairly criticize anything new.
It could also be that a subconscious sense of fear of the original series being overshadowed by the successor (whether due to art quality or natural development - animation quality, new generation of fans, etc) causes them to instinctively attack the successors.
It could be a sense of shared glory in the series they grew up in being known as 'peak shonen' is coveted and causes them to attempt to trash the successor series. This is largely similar to wars between fanbases, except now it is inter-generational
It could also be outside of either fanbases or the artworks
How so?
Well, natural elements could be at play. The fanbases are largely people who have lives. The teenagers of 2013 are now young adults who must work etc. Some of them may have gone into poverty, others may have contracted diseases and even the successful ones may be too busy with work or relationship issues - fact is, in many parts of the world such series are viewed as niche or even cringy interests.
So there can be a great number of reasons why any series falls off in numbers that do not actually reflect the quality of the work itself. That may be why some discount numbers when evaluating such human things as arts, even when those numbers come from humans themselves.
What say you?
