Not the OP but I’m surprised you are surprised this much.

In our 2-person family there are times where me and my wife spend an entire evening, sometimes even a full day or two independently doing whatever hobbies we have. We both appreciate the ability to hyper-focus when we like. It’s very easy to “deal with” too: you just continue your life until the other one becomes available. What is so wrong about it?

You are not uncontactable anyway, if someone needs to contact you they can still approach you. Obviously this wouldn’t work so well with a little kid.