> But wasn’t macOS the only major gaming-relevant platform still using OpenGL anyway?
At the time, there was a decent number of non-gaming cross-platform applications that relied on OpenGL for rendering. OpenGL wasn't perfect (especially compared to DirectX 9) but it was a good-enough solution for simpler apps and games that wanted the write-once-run-anywhere treatment.
> If you’re already writing a Mac-specific backend, why not just write directly for Metal instead of OpenGL?
Because a lot of people don't write Mac specific backends in the first place. Unless the app was designed to be Mac native from the start (a rarity in the professional world), there is very little impetus to rewrite everything to work with Metal and/or AArch64 targets. OpenGL suggested a future world where this would be unneccesary, and people liked it. With Metal as the only option now, a lot of people feel like Apple slammed the door on people that wanted to write cross-platform apps supporting Mac.
> Or, at the least, write for Vulkan and use a translation layer like MoltenVK?
MoltenVK is too slow for games (compared to DXVK it is an utter slouch) so most people don't even bother. There are a few apps that you can run in it, but for the most part it is a toy that rightfully isn't relied upon to deliver industry-standard experiences.
At the time, there was a decent number of non-gaming cross-platform applications that relied on OpenGL for rendering. OpenGL wasn't perfect (especially compared to DirectX 9) but it was a good-enough solution for simpler apps and games that wanted the write-once-run-anywhere treatment.
> If you’re already writing a Mac-specific backend, why not just write directly for Metal instead of OpenGL?
Because a lot of people don't write Mac specific backends in the first place. Unless the app was designed to be Mac native from the start (a rarity in the professional world), there is very little impetus to rewrite everything to work with Metal and/or AArch64 targets. OpenGL suggested a future world where this would be unneccesary, and people liked it. With Metal as the only option now, a lot of people feel like Apple slammed the door on people that wanted to write cross-platform apps supporting Mac.
> Or, at the least, write for Vulkan and use a translation layer like MoltenVK?
MoltenVK is too slow for games (compared to DXVK it is an utter slouch) so most people don't even bother. There are a few apps that you can run in it, but for the most part it is a toy that rightfully isn't relied upon to deliver industry-standard experiences.