While Blackberry’s usage has been decreasing in comparison to the big boys in the mobile operating system space it still boasts of millions of users and because of its security features there are a lot of enterprise who still rely on RIM.
Your business might come from them. Your company might have invested significantly in the devices and the infrastructure.
You might have partnerships and contractual obligations to support these devices.
In cases like these, you would want to give the best user experience possible. And this can’t be possible without providing useful apps.