Window wall for our climate would mean triple pane gas filled likely meaning thicker slabs for structural integrity. Makes sense for an office building, but less sense for a budget residential building. So the windows cost more as does the structure itself.It's amazing that this envelope system (I am assuming this is EIFS) is still cheaper than window wall, when you factor in all the hoarding, heating, scaffolding, and labour required.
That isn't even getting into the insulation conversation of EIFS vs windows. Windows have come a long way with their r-value, but I imagine a solid wall, namely EIFS still offers more benefits for energy efficiency. I'm sure @archited or @kcantor could weigh in with more insight.