Those multi-million dollar companies working on graphics libraries exist. Their names are Epic Games and Unity. Unfortunately, multi-million dollar companies want to make a profit, not give away their product for free.
They have a graphics library inside of a larger engine. And for 99% of devs they don't care about directly modifying such code, so they are fine with the stipulation of "use our tool to get graphics" approach.
Didn't Unity and Epic have people working directly on the Vulkan specification? I remember reading a comment (maybe here!), way back during Vulkan's original release, where someone was screaming about how Vulkan was a conspiracy to make us dependent on giant, multi million dollar game engines.
I don't know about any conspiring, but I've thought about that comment often, because the result appears the same: The barrier to in-house game engine development has been risen further.
I know Unity does, I forget if Epic does but I'd be surprised if they didn't.
Not really a conspiracy so much as the fact that Unity/Epic have much more opinions on what a graphics library can/should be than a small engine developer. The former don't care if it takes longer to release games, they have staff around the clock working on the engine.