basically torch is an huge lib in itself, and it targets not only virtually all cpu architectures, but also multiple gpu frameworks (cuda, roc, vulkan), all off which support thousands of gpus together, both desktop and mobile
and all of this is packaged into a single binary so that it works for everyone, regardless of hardware
if you want a smaller size, you can compile it from source for your specific architecture, or download minimised precompiled versions for your target architecture