@LiveLit maybe to save it for later, so that they can savour the books when they have time. I remember reading a book here on Wattpad. I only read its first chapter and got so hooked to it. But due to my exams, I couldn't read it so I saved it to my library and finally after the exams I read it for like 6-7 times. Later on, the author contemplated whether to keep it or not as she was busy and not too much people were reading it. But trust me the book was worth reading, only if it got three chapters at that moment. I texted the author not to delete the book, even posted a message on her profile and finally I don't know what exactly was the reason but she posted another chapter of it! I was so happy at that time.
Later on, I lost my profile but I was so hooked to reading it again and again as if I'll find something new each time. So, I kept looking through it when I made a new profile. Don't know how many days I've spent on doing so. But I finally got the book and now I have screenshots of each of those four chapters just prior to the author deleting it. Wish she could post more and more!
Ps: I don't remember her id since I just saved the book and not followed the author. Again a stupidity though