From the Hidden Pineapple website:
Unfortunately Rowi has hit up against the user limit imposed by Twitter on traditional third-party Twitter apps so we needed to pull it from the store(s). The user limit is on Twitter's end so new Rowi users would be unable to use the app after downloading it. This is far from what we wanted or expected at any point in the nearly three years of Rowi's existence but we have little choice to move aside and see what experiences Twitter and others can bring to the new Windows* ecosystem.
If you've used Rowi on any device, thank you! You've helped to make it a pretty decent Twitter experience on a platform mostly ignored by Twitter until fairly recently. If you already have Rowi installed it will still continue to work but there will be no future updates. #RIPRowi
There's nothing that Hidden Pineapple can do about the Twitter user limit, which has also had an impact on many other third party Twitter clients. Twitter is, of course, well within its right to impose whatever terms and conditions it deems necessary for its API service, but the user limit has proved particularly contentious, given the impact on the wider Twitter ecosystem and the role played by third party apps in growing Twitter's user numbers in its early years.
It is clear Twitter would prefer it users to make use of official Twitter apps, rather than third party alternatives, in part because it gives the company a greater degree of control over the Twitter experience, but also because it will make it easier for the company to generate meaningful revenue from its users.
Twitter has given more attention to the official Twitter app for Windows Phone this year, but this is a relatively recent development. Longer term Windows Phone users will continue to remember Rowi as one of a number of third party clients that provided a superior experience to the official Twitter app during the platform's early years.