I'm not saying they should be heavier but like LR said, these bikes are built to look a certain way. To keep the look and still get anywhere near the standards of a modern bike with a mild steel frame you need to go thicker and add gussets, electronic ignitions weigh more than points and coils, cast alloy wheels or steel rims and spokes weigh more than alloy rims and spokes, disc, calipers and master cylinders weigh more than skinny drums and cables, tubeless tires weight more than skinny tube tires, electric starters weigh more than kick starters and require bigger batteries, ignition modules and regulator rectifiers add weight, the copper wiring and switch gear that ties all that stuff together adds weight
Modern standards and nekkids are built for performance, the frames are designed to be light and stiff not to look a certain way, the bikes use mostly plastic and alloy instead of steel, it's a totally different set of manufacturing requirements. so no, these bikes shouldn't weigh more but if they were built using chrome molly and alloy like the originals they'd exceed the price point, cheaper materials and modern conveniences equal more weight.