Poorly Made Extrusions
The vinyl extrusion is for all practical purposes the actual frame. At the corners, you see the welds, which can be done well or relatively sloppy. The extrusions have a wall thickness, the thicker the frame the stronger the frame. Certain manufacturers cut production costs by making a thinner wall, which means less strength and worse performance numbers. Less chambers within the extrusion is another way to cut costs, but also reduce the strength and efficiency of the frame.