This could be intentional, as it incentivizes developers to support the Proton version, which makes native Linux support a much smaller leap.

Excited as I am about a big player pushing Linux, we mustn't forget that the intent is almost certainly just to chip away at Windows and the threat it poses to Valve's own monopoly (as a PC game distributor).

A good deed done for selfish reasons is still a good deed done. Frankly I'm just happy to see Linux gaming getting any kind of attention as it's the only reason I still dual boot Windows.

The more charitable interpretation is that Windows as it‘s currently handled is an unpredictable mess that you don’t want to be dependend on.

I think the intent is just to have an out for when Microsoft inevitably kills off the Windows personal desktop, either intentionally in favor of a subscription-based cloud service or through simply making it so crap that extremely desperate people turn to Linux instead.

Valve's behavior suggests that they've never really sought a monopolistic position. Vive was open to everyone, there's no exclusivity agreements with their marketplace, etc. But Steam requires a platform to sell games for, so making sure there's some kind of alternative is in their best interest.

Steam reviews have recently started including "caveat" titles above the reviews themselves, like "Game received for free" or "Presale purchase". I wouldn't be surprised if Valve next added a "Linux version review" caveat.

From a user POV though, I guess proton is an improvement. It means there is a specific windows-like platform called "Proton" that might just about earn a spot in in someone's test matrix.

In that sense, the more bad reviews the better!