A huge amount of games these days are sold as just CDkeys in a box so all of those pesky physical media concerns fall away. You're blocked from reselling them, they're leaden with DRM and the copyright owners are happy.
Even games that were removed from Steam like Hatred could still be downloaded by people who had already bought it.
I think you overestimate how much people are interested in their old games. People just want to move on to the latest and greatest hit.
Because they're bankrupt. Which they will eventually be, the only question is when.