C# and Java have a large base. If you write a small application with it the size will be huge because they both link in the base in the application. It becomes more interesting with larger applications.
I also expect the same for Java, if Valhala ever makes it.
So even though Remedy Games had some experience with D, it is C# that gets all the attention as C++ alternative in tooling and graphics engine scripting, while everything that isn't performance critical in Android (no GC at all), gets written in Java/Kotlin.
These are two good examples of how D lost a potencial market, by always re-inventing itself for the next wave of developers that will finally get D and leave everything behind to adopt it, instead of focusing on having something to make it special for adoption.
For small applications this works even if certain templates can easily lead to have half of the standard library pulled in (e.g a few conversion, a few format, a few regex and boom, the size explodes).
A subset of the language called betterC allows to fully get rid of the "base", but requires to write much more code to get things done. Maybe this is why prakis managed to get the smaller binary ? The comment is not very clear about the methodology...