Blame fucking twitter. URL shorteners have been around almost 20 years now. A quick look at wiki shows a 2000 date. I can recall using shorteners in AIM before 9/11 so that fits.
Linking something to a dynamic API URl that is 100-150 characters long is simply too unwieldy. The direct link to that book was 163 characters long (yes I counted); the fucking twitter character limit was such that you could not link that URL without a shortener. If they had not been around since the early 'Aughts, they would have been invented to fix a problem. amazon, Google etc also use them to track what people are sharing and end user engagement. I'd not be shocked at all if there are people tracking where their short URL's are being posted and making marketing and acquisition decisions based on said tracking.
In other news, Sanderson's universe has been optioned for a movie, and I dread what they will do with his world. So much of the story won't fit well unless they do a very long series. Book one by itself would be two seasons. Game of Thrones had 100+ characters that had to be condensed to save complexity but the stormlight series does not have that out, there are maybe 20-30 main characters.