Actually, Poly, they’re holey not for the weight of the snow, which they probably bear anyway, since a drift can melt into one nearly solid pile.
They’re holey so that the wind can pass through. Imagine gale force winds against several hundred yards of solid sail… ow.
Another purpose of the holes is that it slows down the wind so that the snow being carried can fall out without pushing the wind straight back up as a solid wall would. It keeps the slowed down wind close to the ground.
The same principle applies to dune fences you’d see on a beach. The vertical slats slow down the wind near ground level so that sand particles will then be deposited there.