“Unity is committed to the continued adoption of USD standards. AOUSD is an important step forward to delivering a common foundation for content creation, collaboration and interoperability. We are excited to be involved in the alliance and to help shape the future of USD.” - Allan Poore, Senior Vice President, Unity Wētā Tools
"Epic Games recognizes the significance of USD in establishing standards for 3D content, virtual worlds, and the open metaverse. Pixar has demonstrated exceptional leadership in the open source community over the last decade, and we are excited to witness the formation of the Alliance for OpenUSD, which will propel the technology to new levels of standardization." - Marc Petit, VP Unreal Engine Ecosystem, Epic Games
Gltf isn’t very popular outside of web development. It’s intentionally quite limited to appeal to that demographic, but as a result isn’t as flexible as FbX or USD.
Unity and Epic are both already members, just not at the founders level. The title lists the founders, but there's several more companies at the general level just a little bit lower down the aousd.org page
Unity supports USD -- also Unity isn't technically a content creation tool (well...in the sense of what Adobe and Autodesk tools are). It is way bigger deal for the content creation tools to be aligning on an export format than consumers of said content (i.e. Unity) to align on importer.
