Anthologies make a lot of sense for writers. An anthology is a large book filled with short stories and novellas all surrounded a single subject. The stories are all generally done by different authors, so the readers get a variety of writing styles for one low price.
Financially, it’s great for the author. He puts together a small story that gets put into a print or e-books and he splits the profits with the rest of the authors. It’s not going to make him rich, but it he also didn’t spend a year or 6 months working on it. He sat down one weekend, banged it out and there you go.