This "feature" bothers me a lot. When my girlfriend tries to play Planet Coaster from my account via the family sharing feature, sometimes she kicked off even though I'm not even playing a game at all! I think this is a big reason cloud based services like Steam are a step down from physical games with no reliance on internet connectivity. Truth be told my friends and I were doing fine before Steam existed, even if it meant sometimes needing to get friend's IP addresses and troubleshoot firewall issues to play multiplayer games.

If it's of any help, you can play games at the same time if you go into offline mode in your main account. That way you can atleast play one multiplayer and one single player game at the same time

I'm aware of that workaround but there shouldn't be any need for a workaround in the first place. Valve shouldn't get to freeze my entire library when I want to share a single game with a family member or friend.