To be fair, Nintendo is basically just replicating the system Sony and Microsoft are using for their consoles. But the big difference, of course, is that the Switch is meant to be portable. As I reviewed the Switch Lite, I ended up having to make it my primary system to play digital games on the subway. But that also meant my original Switch was basically trapped on the dock under my TV. This wasn't a big issue for most games, but I was forced to restart progress on games like Splatoon 2 that don't support the Switch Online's cloud saves.
My wife and daughter don't play games (yet!), but if they did, they wouldn't be able to play anything on the docked Switch on their own accounts. They'd be forced to play under my username, which could be a problem when it comes to managing saved games. And, worst of all, they wouldn't be able to play any of my digital games on that system offline.
While multi-Switch households could swap around physical game carts, that introduces a whole new set of problems, especially with kids. Physical games can easily be lost or damaged, and you'll also have to be more mindful about trading games between systems. That's particularly true with the Switch, since each system might be traveling with a different person, instead of being set up throughout your home. Carts are also just annoying to plug in -- sure, that just takes a few seconds, but it's not nearly as seamless as booting up a digital game.