Steam itself does support VR on Linux, but most of the actual hardware (like Meta headsets) don't have drivers for Linux. The ones that do (Valve Index) are buggy, but not unusable. But even then it doesn't get you far, because 90% of VR games won't run on Linux, even with Proton.

So Steam is not the problem. Hardware support and developer support is the problem. Can't really blame developers for not caring, even if they make their VR game work on Linux almost no one would be able to play it anyway, so why bother. It won't get anywhere unless hardware manufactures start making actual drivers for their headsets on Linux. Meta practically controls the market and they don't care, so here we are.