I think one problem is, almost all security cameras are sold with audio these days. If the cameras have a mic, telling people "Oh, we turned the mic off in each camera" or "We don't record the audio" isn't very helpful.
There’s another problem with this because a camera with a mic cable cut would look from the outside exactly like a camera with mic cable intact, and maintenance is a thing, so eventually it’s bound to be replaced by a camera with a working mic either by mistake or “by mistake” on purpose. There’s a trust issue here since people who would be affected by the presence of a mic won’t be able to easily visually verify that it’s disabled.
I saw them advertised "With microphone" or something recently, which led me to assume that was a 'feature' of this model...but you know advertising