We first started using ActiveAdmin in 2014 for a client project and were thrilled with the result and the convenience.
Since then, we have experimented with making different kinds of web applications with Adminterface, including internal systems and admin portals. However, the out-of-the-box styles and functionalities were far from ideal for client-facing systems, and we ended up doing lots of individual customizations. Moreover, we realized that the process of configuring projects became repetitive and time-consuming. Hence we decided to build a gem for it.
It may be odd to some developers out there, but we prefer establishing a standard across all of the projects that we have built. This way, projects will be easier to maintain, less prone to errors, easier to test, and have consistent quality.