Giant say this about bike weights:-
“The most accurate way to determine any bike’s weight is to have your local dealer weigh it for you. Many brands strive to list the lowest possible weight, but in reality weight can vary based on size, finish, hardware and accessories. All our bikes are designed for best-in-class weight and ride quality”
Some other manufacturers do list specific weights for each model and spec eg Canyon.
Personally, I think it would be useful to list comparative weights of their various models and spec options. They could add a disclaimer for legal protection, but Canyon don’t appear to have one. But they don’t list specific bike weights for all frame sizes. They just list a single weight for each bike model and component build spec.