Never seen that done for passengers simply wishing to get off once the jetway is disconnected (just like they won’t reconnect it and reopen the boarding door inside the concourse for late passengers running up who missed it even by a few seconds). A week or so ago I sat at the gate during a weather delay where the jetway was connected and boarding door remained open until our departure clearance was given. Some passengers did get off during the delay period, but that’s obviously different and didn’t inconvenience or further delay anybody else. Weird situation you witnessed.