I think the reasoning (whether correct or not) is that the constant vigilance (such that it is) prevents a torrent of facade from crumbling and falling; it wouldn't just be "an errant" piece.
But our current scaffolding exists because of Local Law 11, which was enacted in 1998. There were some deaths that occurred before that, which is why the law was enacted. But I think the amount of money we spend today to save those lives & injuries is highly out of proportion with out safety priorities elsewhere in the city.
The items you suggest (daylighting, speed control measures, etc) would be costs the city would need to take care of, and require ongoing monthly costs. The power for the street lights, the staff to maintain the lights and do the extra speed control measures, depending on the speed control measures you’re thinking about, it could also mean civil engineers, construction crews, etc. All of this sounds very expensive.