As I understand it, the US inherited a common law tradition from England that empowers judges to effectively create laws. For example the US Criminal code sets penalties for "assault" but a long series of precedents define the actual crime:
> The term “assault” is not defined in the criminal code. Courts use common law to define the term.
> There is no indication in the statute that Congress sought to depart from the common-law definition of “simple assault” when using the phrase in § 111. The phrase is not defined in the statute, or indeed in any provision of the U.S. Code. This is the classic case of a statute importing a common-law term—with, therefore, all of its “soil.”
Judges are usually bound to precedent but can reject precedent in response to novel situations, like the standard of "probable cause" that came out of car stops and searches instead of placing cars entirely in the existing public or private spheres. Policing the Open Road is a great exploration of this.
In contrast Japan (and the state of Louisiana) have a legal system derived from the civil law tradition.
IANAL so I'll defer to anyone that has corrections.
> The US inherited a common law tradition from England that empowers judges to effectively create laws.
Yes, but, in the English tradition (unwritten constitution) Parliament is supreme, and can explicitly choose to supercede any court (or previous Parliamentary) decision.
(The current state in common-law countries varies; Canada acquired a US-style Supreme Court in 1982.)
The dysfunction is a common law system thing due to precedents being legally binding unless overturned. Japan uses the civil law system where legal precedents are not magical spells that control the outcome of a court ruling.
We got used to the courts doing it in America because of how dysfunctional our legislature tends to be.