Good question. Sadly it's all about money. When I produced my first book I printed about 2500 copies, but for the second book I assumed there wouldn't be nearly as much demand and only printed 1800. It turns out I was wrong and that most people who bought the first book also wanted the second. So when I sold out of the second book last year I still had about 400 copies of the first book. So what I needed was to print about 400 Season 2 books to go with the 400 Season 1 books I still have.
So the problem is that printing hardcover books is super expensive. I can get a good deal in Hong Kong, but only by printing a few thousand. Except I don't need a few thousand, since I only have a few hundred of my Season 1 and 3 books left. I don't want to be stuck in a situation next year where I have plenty of Season 2 but no Season 1 and 3. Printing just a few hundred in Hong Kong isn't viable unfortunately. I looked into printing just a few hundred hardcovers here in the US, but the cost was as much as printing a few thousand in Hong Kong. So I decided that the only real solution was to do an affordable softcover short run.
It's not an ideal solution, but unfortunately it's the best option I can think of.