the reason they are so short is the advent of ebooks is also that of novellas. you may have noticed there have recently been many amazing books in the novella format, especially published by Tor. Before novellas were a problem because making them costs as much as any book and therefore they cost as much as any books to buy, as you will know if you bought the physical copy. Now though ebooks are common and this finally allows writers to write novellas. Tor also has very pretty covers and hardbacks that don't immediately run out, which really works for me as I tend to read the ebook first and only if I love it passionately to buy the physical copy. I love the monk and robot series and all her books :)