Yes, but LTO doesn't apply across shared object libraries. Suppose I write a video game that uses DirectX for graphics, but I don't use the DirectX Raytracing

Yes, but LTO doesn't apply across shared object libraries. Suppose I write a video game that uses DirectX for graphics, but I don't use the DirectX Raytracing feature at all. Because of DLL hell, I'm going to be shipping my own version of the DirectX libraries, ones that I know my video game is compatible with. Those are going to be complete DirectX libraries, including the Raytracing component, even though I don't use it at all in my game. No amount of LTO can remove it, because theoretically that same library could be used by other programs. On the other hand, if I am static linking, then there are no other programs that could use the static library. (Or, rather, if they do, they have their own embedded copy.) The LTO is free to remove any functions that I don't need, reducing the total amount that I need to ship.