Or at least we think we know why.

On Friday, as you were heading out for happy hour, we found out that Dropbox had acquired Readmill, a reading app that allows users to do things like highlight passages, take notes and share notes as they read, discuss passages and so on.

Let’s take a look at what Readmill was -- and yes, we’re using the past tense intentionally -- a beautiful, much loved social reading app that Dropbox will be shutting down and absorbing. Check out the “auf wiedersehen” from the Berlin-based company:

Readmill’s story ends here. Many challenges in the world of ebooks remain unsolved, and we failed to create a sustainable platform for reading. For this, we’re deeply sorry. We considered every option before making the difficult decision to end the product that brought us together.

As of today, it is no longer possible to create a new account, and on July 1, 2014, the Readmill app will no longer be available. For the next three months, our first priority is to help you transition to other services and get back to reading. All of your books and reading data are available for export in multiple formats.

Our team will be joining Dropbox, where our expertise in reading, collaboration and syncing across devices finds a fitting home. Millions of people use Dropbox to store and share their digital lives, and we believe it’s a strong foundation on which to build the future of reading. We’re delighted to work alongside this talented team and imagine new ways to read together.

Thank you for the time and attention you’ve contributed to this community. It has been a privilege to read together, and we look forward to meeting again, in new ways, in the margins.

Why Would Dropbox Want a Social Reading App?

If you’re wondering why Dropbox would want a social reading app, the reality is that it doesn’t -- at least not the part that has to do with books. That’s why it’s shutting Readmill down instead of hosting it under its own roof.

What Dropbox does want is Readmill’s technology. It offers beautiful HTML-based reading experiences, analytics, and facilitates collaboration and syncing across devices.

It shares some of the same functionalities as Box’s Box View, which Box introduced during its developers conference last week. Box acquired Box View’s capabilities through its purchase of Crocodoc.

Dropbox’s newly acquired technologies will be aimed at the enterprise.

We also expect that Readmill’s founders/developers will be busy with the Dropbox/Readmill integration as they are reportedly moving from Germany to San Francisco.

This Isn’t Dropbox’s First Collaborative Purchase This Month

Earlier this month, Dropbox acquired Zulip which was still in stealth (closed beta) mode at the time of the purchase. According to TechCrunch,

Zulip had already developed a suite of applications for Mac, Windows, Linux, iPhone and Android, which allowed users to share both public and private messages with their co-workers. Public messages would appear in 'streams' related to the topic at hand, like 'Design,' 'Sales,' 'Support,' and more, for example.”

Dropbox is Catching Up Quick

In last summer’s Forrester Wave for Enterprise "File Sync and Share Platforms,” Dropbox ranked two levels below Box, EMC Syncplicity and IBM’s Connections, and a level below Citrix, Accellion, Egnyte and WatchDox.

But change in this marketplace can happen very quickly. Consider that EMC Syncplicity wasn’t even on some analysts’ radars in 2012 - early 2013 and that it was listed as one of Box’s main competitors in Box’s S-1 pre-IPO filing earlier this month.

If Dropbox stays serious about its enterprise play and makes its way off of the enterprise IT blacklist (Box is on it quite often as well), then it stands a good chance of joining the leaders in the enterprise file sync and share space. It already has something going for it that no one else does -- the love of 200 million individual users.