A-frames are steeply-angled enough that the weight mostly loads on itself (i.e. a snow drift builds up against the side of the house) rather than loading the roof. The whole point of the design is to be steeper than the https://en.wikipedia.org/wiki/Angle_of_repose of snow, so that snow can't pile up on the roof to the point that it forms ice; it must slough off quickly, as soon as it reaches some aggregation threshold — just like water droplets must drip down off a shower door after some aggregation threshold.
("Slow" snowfall, meanwhile, gets melted away rather than frozen on; the A-frame is the entire building envelope, and is also usually made of a highly thermally-conductive material; together, these properties mean that 99% of heat lost from the interior is lost into this giant metal heatsink that wraps around the building, where the heat then conducts quickly inside that giant metal heatsink, warming up whatever cold spots there are anywhere along its surface. As long as the building has any kind of heating going on inside, the roof is essentially acting like a heated windshield.)
A-frames also go all the way to the ground. There's nowhere for a person to stand where "snow (or even ice) sloughing off the sides" is dangerous, because there's never a plummet phase to that slough-off; the snow arrives at the ground with very little speed, having been lightly friction-braked the whole time, since it was basically sliding down a metal slide. (That being said, you would never build an A-frame house under the expectation of having accessible sidewalks around it during the winter. You assume that snow drifts will pile up on both sides. You want to go to the back yard? You go through the house. This is also why you never see an A-frame surrounded with a fence: the inevitable snowdrift would knock any side-fences over.)