I have spent a somewhat ridiculous amount of my time working on making games smaller (it's a hobby). And have come to the conclusion that very few things make games so big: DX11 only supports textures in a somewhat uncompressed format so the CPU doesn't bottleneck load times, however vulkan has had something called basis universal which makes textures infinitely smaller and faster loading. Another thing is old formats (especially for meshes) and most importantly bad design. For example ark survival evolved can be two times smaller if you check for redundancy of files (I think their settings system for unreal assets is broken).