Overall sales might be up but are those sales making the head fatter, the tail fatter, or the tail longer? For any individual writer without sales in the head, increased sales only matter if the tail gets fatter. They don't individually make any more money if it gets longer (more books by more writers).
As long as the writers are making enough money to produce their best output, the ideal situation is as long a tail as possible. The greater the variety of author, the greater the variety of books.
But that's the core issue. A long tail is good for Amazon and theoretically good for readers. It's not really helpful for writers. Any in the long tail are unlikely to ever pay back an advance and actually make money off sales let alone be making enough to produce their best output.
So total unit sales being up doesn't necessarily counter that statement "no one reads books anymore". Unit sales being "up" has a lot of qualifiers.
