The first reason is for the authors. Whether to keep their ratings good because Amazon deletes positive reviews after six months and not negative reviews, to build good ratings of a book in the hopes of building a reader base, or because it just feels good to now you are appreciated.
The second reason is because I am forgetful. I can't count the amount of times that I have read a book, then months later remembered some anecdote from it or wanted to check and see if the next book in the series was out yet and couldn't remember the book or author. It's extremely frustrating and I'll wrack my brain for days trying to remember what is, in the end, a pointless exercise in recollection.
Of course, it doesn't help the sheer quantity of books I read in a given time period. I read an article that said a "prolific" reader reads at least thirty books in a year. That equates to less than a book a week. I've read more than that in a three month semester before. While taking a graduate level class. And working 50+ hours a week. Based upon my reading habits, I would say that my read total for a year's time is probably closer to 180+ books a year. What does that make me? An obsessive reader? It's not uncommon for me to finish a book in less than a day.
Now granted, I go through slow periods. Recently I had a period where I hardly read a thing for a week or more. I had rotations for graduate school, exams, and papers clogging up my time and simply couldn't free up the time to go anything else. But after that time, I think I spent three days straight doing nothing but reading and finished maybe six or more books.
I've also gone through spells where I ran out of books I had planned to read in a given genre (I tend to have specific genres I feel like reading at any given time - my current genre is paranormal fiction). After reading at least fifty books in less than three months, I exhausted every book I could find of NYT bestselling vampire fiction. I'd had a list of authors I had wanted to read and completely wiped it out and found myself at odd ends not knowing what to read next. I ended up rereading things.
Well, off to continue reading The Forever Girl by Rebecca Hamilton. I plan to write the review for that novel on Friday so see ya soon!