There's the big ones like Unreal, Unity, etc. The same is true of smaller in-house engines I've seen and worked on. Even open source hobbyist-driven engines like Godot have multiple renderer backends.
It is true that there is a fair amount of translation going on (browsers and ANGLE is a big example, along with the recent MoltenVK) but it's by no means the only way people do things.
KSP, factorio, prison architect, they all put considerable efforts into native linux support. I'd hate to see that be outsourced to valve's compatability layer(s).
Nothing prevents developers from making specific Linux clients. Valve just provides the option for when clients are not available. Nothing to lose, really.
The way I see it, devs aren't obligated to support any system they don't want to. I really appreciate the ones that take the time to support Linux natively, or even by using an emulation layer because I realize they don't have to. If this makes more developers realize Linux is a viable ecosystem for them to make games for. Even if it's just through an emulation layer to begin with at least they're making some efforts which is more than can be said less than a decade ago.