In 2014, when Apple introduced the Metal graphics API, the landscape of computer graphics APIs was dominated by long-established standards like OpenGL. Seismic shifts were afoot, however, with the announcement of DirectX 12 a few months prior and the initiative that would produce Vulkan starting to take shape. These parallel efforts signaled a significant shift away from the accumulated cruft of 20+ years of OpenGL and other APIs born during the fixed-function era of GPUs.
Source: A Decade of Metal: The Early Years (2014–2019) – Metal by Example