For your first book you are so grateful that you will accept whatever is offered you. That was my case with "Sho: Japanese Calligraphy." I had published it privately and then Tuttle made me an offer for the copyright; there was no down payment and they screwed me for 2.6% royalties for the biggest market, USA. The company has been bought by Periplus, but I doubt I will ever ask Tuttle to print any of my books again.
Of course publishing is a business, but the author also has bills to pay. With Japanese publishers they want an MS that is ready to print without any editing. In reality this is not possible, because books are published in reams, and having the wrong number of pages means a waste of paper at the printer, so the publisher will edit the book to fit a ream.
Nowadays many books are returned from bookshops unread, and the publisher then has to reimburse the wholesalers &c. An average book has a 20% return, a 10% return is considered a success by the publisher. So you would expect the publisher to market the hell out of new books, but they do very little. It is the Pareto ratio all over again; 20% of the books are by well-known authors or safe authors, the other 80% is a gamble. Now publishers in Japan have gotten themselves in such a difficult position with returns and a declining readership that they have to continually publish to stay afloat. Something like a shark that continually swims so it can breathe.
Now my books earn a 10% royalty, which is okay, but then I also have to pay for the translation (not the publisher), and I have other expenses such as paying for images that have a copyright, such as Getty Images.