A relational database design uses an entity (table) for each logical groupings of tuples (rows: people, places, things). It follows then that each foreign key relationship between tables is a specific foreign key. For example, a relational database with about 50 tables might have 50 different foreign keys.
So the answer to, Why a Graph Database? is that TejonDB is designed to be highly configurable and flexible, and the graph database design is extremely flexible - much more so than the traditional relational database. (as a side note, I designed the initial pattern for generalized connections while experimenting with sentence structures for data, several years before I heard the term graph database. The pattern is just that intriguing.)
TejonDB takes it a step further by adding object-oriented structure and usage rules to which classes (types) and statuses (statuses), because just adding a label to a node or connection is too slippery for enterprise use.