There was a time when DRM was only visible when it broke your legitimately purchased game (e.g. SimCity, Diablo 3)
Now at least gamers are getting some decent perks from DRM (e.g. digital loaning, play anywhere, cross platform licensing) so it's a bit easier to stomach.
That's because people have been vocal about that. If the companies had it their way, I'm sure the majority would want you to buy a new license for each platform and system (like how the cheap Windows licenses are - locked to your system)
The old way of doing business was proprietary everything. (See Sony in the 80s and 90s) I'm just glad manufactures finally saw that locking things down so much increased customer anger and frustration more than it increased sales. Being a child of the 80s, I'm still surprised at stuff like using a generic USB thumb drive in an Xbox 360 and things of that nature.
* Windows falls out of popular use for residential people / People moving away from using PCs as we know it.
* Steam client not being available for the mainstream OS of the day.
* Most of the games in your library not working with the the mainstream OS of the day.
* A new platform replaces Steam and it has newer remakes of classic games.
* We are all in our 50-60s and lost access to our accounts long ago because we don't play games anymore.
Steam probably won't be killed off in one day. It will die gradually as it falls into disuse.