Do you wonder why Blender doesn't support the DWG file format? As it turns out, it's an issue with the GPL license of LibreDWG
Alexandre Prokoudine writes:
If you care about things like CAD, precision modeling and industrial design, you probably wondered why Blender doesn't support DWG that's practically a de-facto standard in the industry. Contrary to a popular belief, it's not just because DWG is a proprietary format.
Libre Graphics World published an in-depth study of the subject that contains an interview with developers of LibreDWG, a GPL library for reading and writing DWG files, and comments from a representative of Free Software Foundation and developers of end-user software, including Ton Roosendaal and a developer of Blender-compatible Open Assets Library.
The result could be summarized like this. LibreDWG is the only library that allows free software to implement support for DWG files. However there are several reasons why it's not really used anywhere beyond GRASS.
1. It's license (GPL v3) prevents most applications like LibreCAD, FreeCAD and Blender from using it. FSF who hold the copyright for it used to be unwilling to change the license and preferred 3rd party software to stop using components that prevent an upgrade to a license compatible with GPL v3. At the moment FSF is in conversation with developers of LibreDWG regarding a change of license, but no clear statements have been made yet.
2. The specification of DWG issued by Open Design Alliance used to be very far from being complete and only started gaining essential missing information last year, after development of LibreDWG ceased.
3. Both lack of adoption of LibreDWG by end-user software, lack of information in the spec and lack of time were the reasons why development of LibreDWG ceased a year ago.
4. 3rd party developers are interested in supporting DWG if the license of LibreDWG is downgraded to a more liberal GPL v2+ or the like.