The thing that remote “pop in” doesn’t do is let me assess how interruptible someone is. When I pop in on someone in an office, I do it when I’m not interrupting their deep work — it’s extremely easy to tell when this is. Remotely, it’s much harder.
"When you are online and able to be disturbed, you join your office, alone."
In the office scenario, I as the interruptor take on the burden of finding out when someone is open to being interrupted (and it's not that hard). For example I can just say "I'll ask him the next time I see him" and wait until I see him go to the coffee machine or the bathroom. Or, if it's more urgent, I can take a peek in his office and see if he seems to be engrossed in thought or more relaxed.