By "base system", I didn't mean what you can achieve through tweaks. I meant what you end up with after a default install. I'm talking something like a vanilla openSUSE KDE install that comes with a full desktop environment; a web browser; and graphical applications including a file manager, a complete office suite, an archive manager, multimedia players, a text editor, a photo gallery, a local music player/manager, a package/update management frontend, system settings app, fat email client, etc.
The primary factor isn't that Linux distros can include fewer components, it's that traditionally they actually make proper use of shared libraries because everything installed on the system is part of a single software distribution with a unified dependency tree.
I say "traditionally" here because distros that use Snap or Flatpak for applications that ship with the OS as part of the "base system" introduce massive redundancy in a similar way to macOS. That's why I chose openSUSE for an example rather than Ubuntu.
But you can get something like a 1:1 comparison if you compare install media (which is typically compressed) to install media. Linux distro installers and Linux live media often still fit on a single DVD:
• openSUSE Tumbleweed Live (GNOME|KDE): 1.2 GiB
• openSUSE Tumbleweed Installer (can install KDE or GNOME, plus optional applications): 4.4 GiB
• Fedora 44 Workstation (GNOME): 2.7 GB
• Fedora 44 KDE: 3.1 GB
• Ubuntu 26.4.0.1 Desktop: 6.0 GiB
• Windows 11 25H2 ISO: 8.4 GB
• macOS 27.0.1 InstallAssistant.pkg: 18.4 GB
macOS is more comparable here to the Linux distros than to Windows, because it comes with a more complete suite of end user applications than Windows does. It's also true that Linux distros are really good at compression when it comes to installation media and live media. But the other piece that I think is clear from these (AI slop, feel free to gather your own) numbers is that traditional Linux distros just make better use of the space in terms of the ratio of number of graphical applications to total disk usage than macOS or Windows do. They have dramatically smaller install media and dramatically smaller base installs than Windows,
even though they come with an application suite more comparable to that of a Mac. macOS meanwhile just uses a ton of space both for its install media and its base installs. The difference is in significant part due to the benefits a unified software distribution offers in terms of resource sharing across packages/applications.
That's all completely aside from things like non-graphical installs or foregoing applications like an office suite (let alone foregoing a whole DE). Distros that actually try to optimize disk usage like you're suggesting end up with disk footprints way smaller (e.g., a 792 MB installer image for PuppyLinux, 1.3 GB for Bodhi Linux 7 Standard, 694 MiB for DSL 2024).
This benefit is also the footgun that let Linus Sebastian of LTT (in)famously uninstall his desktop environments with a careless package management command. Applications and the base OS form one system with heavy internal dependency sharing.
Things like app bundling and containerization have lots of advantages, especially when it comes to deployment. But they also have costs, and relative to a normal Linux distro with just one package manager, disk usage is a huge one.
The above also gives us another comparison for macOS 27: just the new machine learning models alone take up more than enough space for a complete, modern graphical operating system AND a graphical end user application suite.