Why does my zoom audio, when there are nearby microphones, seem to usually take an open loop format?
This effect is usually undesirable and is prevented by (acoustic) echo cancellation algorithms. These algorithms estimate the distortion of the incoming signal on its way to the microphone (via the loudspeaker and the room acoustics). That distortion is modeled by a filter and the output of that filter is subtracted from the microphone signal, such that the contribution of the incoming signal to the outgoing signal is minimized.
Zoom has an option to turn off echo cancellation, so you could try playing around with that.