They selected a middleware, Coherent UI, that didn't work properly on anything but Windows. They also didn't make proper use of the Steam runtime, a mistake that continues to cause issues. Most games don't make these mistakes, so this isn't really representative of the larger state of Linux gaming.
It's worth pointing out that the devs did make a legitimately good attempt at making Linux/Mac support first class, by making a purely OpenGL engine for the game. But it seems they weren't aware of some other best practices.
They selected a middleware, Coherent UI, that didn't work properly on anything but Windows. They also didn't make proper use of the Steam runtime, a mistake that continues to cause issues. Most games don't make these mistakes, so this isn't really representative of the larger state of Linux gaming.
It's worth pointing out that the devs did make a legitimately good attempt at making Linux/Mac support first class, by making a purely OpenGL engine for the game. But it seems they weren't aware of some other best practices.