This is for native AOT binaries, not for the typical case. Though this release and the previous ones did contain improvements for trimming binaries, which is what you need to use to make non-AOT binaries smaller.
Curious - why isn't it the typical case? .NET runtimes on Linux itself are rare enough, I figured AOT on Linux would be about the only use case, especially in containerized environments.
The reason that they are unaware, mostly is that using NGEN requires really wanting to use it, as it requires dealing with strong named Assemblies, aka signed .NET libraries/executables.
It only supports dynamic linking, and still pings back on the JIT for more complex code sequences, its original goal being fast startup time for desktop applications.
Thus before .NET Native (UWP only), Mono (iOS/Android), and now Native AOT, doing AOT compilation on .NET was largely ignored, despite NGEN being available.