it's just the chicken-or-the-egg problem in regards to Linux support for games.
Well, given the current repertoire available for Linux on Steam :
it's more like there a giant flock of tiny hummingbirds who are happily laying eggs all together in Linux nest.
Only a couple of huge ostriches are too smug to lay their giant eggs there, or are only able to lay hideously deformed linux eggs.
There are currently thousands of Linux games on Steam. Most are indie games.
Of the triple A big studios, only a few run on engines that already have good Linux ports (hi, Ryan Gordon !)
The rest are either doing extremely crappy ports relying on aweful middle-ware for the windows-to-unix adaptation,
or completely ignore the non-Windows/non-DirectX market.
That's a gap that Vulkan could eventually close one day:
unlike the OpenGL vs DirectX opposition, Vulkan is the same API everywhere.
Including Windows, including Linux, including other hardware.
Also, Vulkan *drivers* are much lower-level and simpler than OpenGL or DirectX (because most of the advanced management is moved out of the driver and into the game engine. That's the whole point of giving low-level access to the devs : to help them have better control on the hardware by letting them handle all the small management details) - that also means that the Linux world can produce Vulkan drivers at a faster pace with less bugs (see the fully open-source RADV driver for Radeon hardware). Less playing "catching up" than current OpenGL revision in Mesa or DirectX compatibility layers in Wine.
And for game makers, it means most of the heavy optimisation done in the game engines (and these are going to be much heavier optimisation due to the bigger role played by game engines) can be leveraged much more easily on anything running Vulkan (that includes Linux and Valve's SteamBoxen) than used to be before (where a DirectX-developped game engine needed to be ported to whatever runs on the port target. Means usually rewriting the engine to run on some PlayStation's low-level API. And a Mac OS X/Linux port means yet another rewrite to OpenGL)