I'd thought Steam not offering a subscription service points more to Valve being ossified, or Valve having enough insight to know it is a terrible business move

I'd thought Steam not offering a subscription service points more to Valve being ossified, or Valve having enough insight to know it is a terrible business move and will lose money in the long term. It would not be much effort at all to allow publishers to opt-in their titles, and they already have all the playtime metrics to share out revenue and DRM to control access. The biggest headache would be picking a price point and the revenue sharing algorithm, much like Amazon with its ebook library subscription.