OpenGL is the only other open source alternative. Vulkan is developed by the folks who created and manage the OpenGL specification. (https://www.khronos.org/) To shorten the list of differences I will specify one. OpenGL is ancient and can not compete on modern hardware. Vulkan is the new hotness that everyone in the future will support.
There are a many reasons that more fully answer your question but this is the short/fast.
OpenGL is the only other open source alternative. Vulkan is developed by the folks who created and manage the OpenGL specification. (https://www.khronos.org/) To shorten the list of differences I will specify one. OpenGL is ancient and can not compete on modern hardware. Vulkan is the new hotness that everyone in the future will support.
There are a many reasons that more fully answer your question but this is the short/fast.
I think it’s more that opengl is a higher level API that offers less granular control in exchange for easier cross platform support.