Habeas corpus comes from English common law, not Roman law. It was never used in German law.
Latin terms are still used in German legal writing. Just not this one.
Well, perhaps we can congratulate the German-speaking countries for throwing off the yoke of Latin!
It did not happen in the Anglosphere because England was run by the Normans for hundreds of years, during which the common law system grew enormously...
Let's also not forget ecclesiastic Latin! Significantly less common in the HRE since Martin Luther's protestations!
The fact that the language has such a degree lf these holdovers has something to do with Americans (or, rather the Anglosphere more generally), which is why the GP can note that it is a difference from German, where once upon a time; Germany had the same use of scientific, clerical, and professional Latin in the past, after all.