For one thing, Vista onwards includes the entire system on the hard drive, including optional drivers, language packs, features, etc, so you never get the dreaded “Please insert Windows setup disc” prompt. This also makes Windows setup a bit faster as it can for the most part just install one big disk image.

Another factor is 64-bit Windows, which became mainstream with Vista. 64-bit installs include both 64-bit and 32-bit system libraries, so it takes significantly more disk space. This is still the case with Windows 10, which might explain why some low-end devices still have 32-bit pre-installed.