Flexibility, parameterisation, re-use, variety, masses of content, small data, scalability. Endless, rich content creation, allowing smaller teams to create greater quantity of content.
Why visual editing?
Visualisation of information flow, not text based, multi-output, immediate feedback. No compilation, interactive, easily enhanceable through tool improvements.
Why own engine?
Many of the features Apparance is built around require approaches not supported by conventional render/game engines. These include: Unified meshes, dynamic mesh building, full-scale generalised detail blending, diverse level-of-detail strategy, background synthesis, procedural/run-time shaders, continuous world, scalable entity behaviours.
Many games studios develop and maintain their own engines that are better suited to their games than the general purpose middleware solutions available.
Why no plugins?
A lot of people use Unity, Unreal, or other 3rd party engines to build their games. The reason Apparance isn't targetting them is a drastic mis-alignment in the way the engines work. Conventional engines are level-based, limited size and scale of their worlds, and at a number of levels aren't geared to support procedural generation well. For example, mesh rendering is not designed to be dynamic. Also, nav-mesh and collision systems aren't very dynamic content friendly. It's understandable that optimisation has focused on the traditional pipeline, but proc-gen requires effort to support it well. Update: Since this may be the best way to open up the potential audience and customer base, by gradually introducing some procedural techniques into a familiar (and comprehensive) game development environment, it warrants some more investigation. I'm going to start some experiments to determine exactly how well Apparance technology can be integrated into Unreal. This direction seems the most sensible way to explore as I have fairly decent practical experience with UE4 to back it up. Watch this space...
Why doesn't it have <insert graphic feature>?
Largely an issue of priorities. Many graphics features are planned; advanced lighting, shadows, texture support, materials, and so on. These are all 'solved' problems in game development where-as the novel features of Apparance are not and need to be the priority. Since these are also not generally my area of expertise, it's worth waiting until resources are available to employ actual graphics engine engineers to handle this side of things.
Why only this platform?
Again, a matter of priority; porting is going to be possible, but also not my area of expertise. Once there is enough interest in the project and resources available, the porting process can begin.
I want to work a particular way, embracing interactivity, intricacy, immediacy, and play to create games. The tools to do all these things don't exist, so I decided I would build them.