I sometimes play games that are many decades old, and as anyone that collects games knows, consoles tend to live shorter than physical game copies.
So what am I going to do with a Xbox One in 20 years after the DRM Server were turned off?
Hope that the console never fails so I don't lose my complete collection? (If the failure rate for the last two Xbox generations is any indicator, chances are slim)
Thats one thing steam is actually pretty good for, its got lots of older games (some from the early 80s!) that generally just work on pretty much any modern PC.
Also, it's probably much easier to backup and play your Steam games on a PC, even if Steam wont be there forever, than it would be with such a locked up system like the Xbox One.