Maintenance and backend version updates of phpBB had become increasingly problematic for us over the years, so our primary goal was to move towards a hosted solution that still permitted the necessary level of single-sign-on integration. Security and antispam protections were also important aspects that phpBB has always struggled with.
Discourse is a modern and actively-developed offering that is being used by an increasing number of other forums and it has all of the major features that we were looking for. Since it is a hosted solution with commercial support it actually reduces costs for us by not requiring us to dedicate our own IT staff towards maintaining it (which none of our IT staff actually wanted to do, nor enjoyed doing, because of its fragile backend nature).
We recognize that the user interface is significantly different from phpBB, but we hope everyone will take the time to learn the new environment and recognize its strengths. We will continue to tweak some of the styling and settings that are available, so things may continue to improve over time. Thanks