I think what it certainly means is they've looked at the analysis of how the traditional family sharing has been working. And they see lots of geographically dispersed groups sharing libraries.

I have a credible source tell me the original idea was that parents and children could share libraries. Because having multiple children and repurchasing your library multiple times is a burden for families.

I think they've both improved the system, by allowing games to run concurrently, and reduced the unintended usage of their household sharing program. A program that only exists by the good grace of the publishers, by not being a threat into game revenue. If you can make the argument it's a family sharing, and they would have bought the game once anyway, then it's not a problem to share the game.

I think they took the minimal cut that made this work, they could have done something ownerous like require everybody to upload IDs and prove a family relationship. But that wouldn't scale, and it probably exclude lots of different odd family scenarios. This way they're very inclusive. The only limitation is geographic pricing boundaries. They don't want the one family member in Ukraine buying games for their distant family in the US at a discount. They are trying to do geofencing of the pricing.

Like you said, if it is a big problem for adults, they can just pirate the games. Steam's trying to make it as convenient as possible for a household to not have to repurchase games without becoming a pirate