Not counting those folded in a crash, the new wheel taco is best understood by imagining a ball cradled at th Ed top of an M. It stays put because it has to go uphill in either direction before it can fall off.

Likewise, a built wheel is stable because moving the rim to either side would increase the tension of spokes on the opposite side. Once past the point of no return it will taco, because that condition has the lowest total spoke tension.

However a highly dished wheel is like that ball balanced on an M with a low side. So, comparatively less force is needed to push the rim past the right flange and cause a taco. Not high tension, but uneven tension can leave an area not well braced, and prone to taco.

IME, I've seen this happen when builders get carried away stress relieving newly built wheels, but never without some help to start the process.