You can do that, actually. It has some pretty big caveats, but if you are not actively playing anything on Steam then your library can be lent out to others... all you have to do is sign into their computer using your Steam credentials.
The frustrating thing is just that I cannot play free games on my steam account (hi dotas) whilst lending a paid game to ma famile.
For example, I would pay $200+ to watch Tennis Opens, but I need it to be a simple transaction and 1 click to watch the game from the schedule page on the tennis association website.
I suspect there are so many great deals on Steam specifically because it's not possible.
If I'm going to the trouble of exposing a VPN service over the internet for my friends, it's not so I can also pay for a streaming service.
I remember growing up it would be really common for people to split the cost of a PPV fight and VHS recordings would be passed around. It seems pretty similar.
Community-based media sharing is great. I wish it was possible for me to lend all of my Steam games when I'm not using them.
[0] https://www.youtube.com/watch?v=9CunwUs08og