According to an article by The Bookseller, Susan Jurevics, Pottermore's CEO, had essentially three reasons. We might argue over whether or not they were good reasons1, but these are hers:
They don't think gamification is the right approach for their core audience:
Jurevics told The Bookseller: "When Pottermore first started, it was positioned for the next generation of readers, and that next generation was almost by default tagged to be children. So the current site gamified the content, making it very simplistic in terms of collecting things and casting spells. That was appropriate for children, but that wasn't actually the core audience." Jurevics said that the user base was “overwhelmingly young adult and female"
It uses the web more effectively:
The relaunch also reflected technological advancements in the way users now access content sites, Jurevics said: "From a technology point of view, when Pottermore was designed and conceived the iPad had not yet been launched, and the population didn't yet sleep with their phones on. The current Pottermore is really a laptop or desktop experience and that type of usage is going away." The new site will be smartphone-first to reflect this "fundamental change in user behaviour", with content designed for touchscreens and swiping.
[...]
For the first time, the site’s content will be made available to search engines and indexed, with additional content derived from numerous sources including filmmaker Warner Bros and other franchisees.
I didn't have a lot of involvement with the original Pottermore, but from my limited experience it had a number of limitations in this area:
- Heavily flash-based. This is a geek's argument, so I won't delve into it too deeply, but flash is a horrible tool for websites to use, and is especially unfriendly to mobile devices. I have a pretty old laptop, and the old Pottermore made it beg me for death; I shudder to think how it would have gone if my main computing device was an iPad
- Content was not shareable. Not long after the new site went live I went and updated as many of the links to Pottermore content on this site as I could, and I was astonished at the hoops we jumped through to include citation links: Slytherincess probably has about half of the old Pottermore on her Flickr account, and there are/were at least a half-dozen fansites dedicated to archiving the content in a linkable way. The only way to cite things directly from the old Pottermore was to include the name of the Moment, which required someone to sign up for an account and then track that Moment down
- Navigation was tedious. If I remember correctly, Moments you had already unlocked could be reached from a single homepage menu, but finding new content required hunting linearly through the narrative. I recall plenty of furious clicking after I signed up for an account, searching for a particular Moment for information I needed to cite in an answer here
It's more flexible about content, allowing material not tied to the narrative:
Perhaps the most significant shift is the removal of the central concept behind the original site, which required users to become students of a virtual Hogwarts in order to progress through the books and experience the site. Jurevics said the change reflected the way the Harry Potter series had now evolved outside of the core seven books.
She said: "[J K Rowling] finds these corollaries in the real world and evolves the magical world through a lot of the new writing, for example when she created the Quidditch World Cup.
But in the very linear narrative—focused on the books—that we had, there was no place for that. She can now write content that is about the wider wizarding world, but is not anchored to books one to seven."
As we've seen, it also allows them to include other types of content, like news updates, and illustrations
In the same article Anna Rafferty, Pottermore's director of product, creative and content, gave another reason; decoupling Pottermore from the linear narrative structure of the books makes it more accessible to more levels of fan:
Rafferty said: "We are opening up all that content—this world is expanding and we want people to have access to all of that, whether they are superfans or not. It is no longer a linear experience. It's not a book. You don’t read a website from the home page to chapter one to chapter two, and we needed to reflect that. There are going to be hundreds of thousands of landing pages. It’s an immersive world, but one you can rummage around in."
1 Personally, I think they're excellent reasons. The issues I have with the new Pottermore are almost wholly unrelated to these reasons