Steam DRM is trivial to circumvent, it’s basically cheap locks screwed onto the game with security torx, not even riveted: If you have a toolbelt you’re already in and every skiddie with half a brain cell can do it as Valve doesn’t bother defeating the scripts that are floating around.

What it does prevent is random tech-illiterate people copying game files to their friend’s box.

If Steam dies one day then my library would be largely lost, yes, but not due to DRM but because most of my library isn’t actually on my disk.

Not really, no. Those keys are more or less equivalent to a browser’s user agent, difference is you don’t choose your own but get them from OpenSubtitles. Motivation probably ranges from “that makes it easy to reject random crawlers” to “we’d like to know the people writing software against our API, or at least have a way to contact them”.

You’ll also be able to find examples of such keys in repositories in the future in case you don’t want to request one of your own but frankly speaking that’s a dick move.

Also if you want an “our way or the highway” attitude you can buy a PC, install a gnome distro, and not pay like 1000 bucks more for 16G more RAM that you won’t be able to use in another machine because Apple locks everything down for reasons that definitely don’t involve unadulterated greed.