[brlcad]

Working with solid geometry and boundary representation structures is immensely more complicated and affects everything from dev velocity to GUI design to usability to acquiring devs. Content modelers (e.g., Blender) deal with considerably simpler geometry representations that are not typically valid or easily verifiable for engineering purposes. That's why it's very non-trivial, decades worth, to turn something like Blender into a CAD tool. Even seemingly simple features like CAD converters can take years of effort. BRL-CAD's primary investment has been on geometric analysis (e.g., solid ray tracing) and it's unparalleled in that regard, but that's a niche audience without better usability.