I have no idea if this is true everywhere but at some point in the US in the last 15 or so years they switched to hollow, particle board legs which will only really hold weight if you bolt all the way through with nuts and you still have sag. You could replace the legs with your own solid wood but at that point you might as well just make your own lack from scratch.
I remember lusting after my own in the early aughts and finally tried it years ago with disappointment.
