More immediate response to disconnection.

Rather than "IDK keep sending but I haven't heard ACK in a while"

When the disconnection is brief, there's no need to respond to it.

It's the conceptual equivalent of your phone "helpfully hanging up" when you change the phone from one ear to the other during a call.

It's the conceptual equivalent of your phone helpfully hanging up when you turn on airplane mode.

Turning on airplane mode explicitly signals "sever all communications" in a way that making a quick adjustement of an ethernet plug does not.