That loops back to the "Facepunch doesn't believe they have the technical expertise/manhours available to support Linux users so therefore simply provides refunds to prior Linux customers and a 'no support but not antagonistic approach' to Proton/Wine users" problem that they've found themselves in. I would imagine internally, if they flipped that hypothetical switch, it would be seen as them committing to provide Linux support again (which they've admitted they aren't prepared to do).

From their perspective, it's better to just allow Proton users to play but not allow them to join "official servers" or community servers with the existing EAC so they aren't accused by the community (I know, we suck sometimes) of "allowing Linux cheaters to fly under the radar". They also won't have to handle their support tickets, I reckon, and can just provide a refund if needed.