Why did you not use ZGC or Shenandoah?

The choice of garbage collector depends on the project requirements and the runtime environment. ZGC and Shenandoah are modern low-latency garbage collectors that minimize pauses, but they may have increased memory consumption or be less stable on certain JVMs or versions.

Possible reasons not to use ZGC or Shenandoah:

• Compatibility requirements with the JVM version used, where these GCs are not yet supported or are unstable.
• The application does not experience GC pause issues, and the current collector is satisfactory.
• Memory constraints or other system requirements where ZGC/Shenandoah are not optimal.
• The need for predictable behavior, where a proven GC is preferable.

Thus, the choice of garbage collector is a trade-off between delays, resource usage, and stability, and the decision is made based on the specific conditions of the project.