Maven container fails to detect CPU cores

When building a Maven project with pipelines in maven:3-jdk-11-slim container it fails to detect number of CPU cores.

The number of processors were checked with a pipeline step

grep -c ^processor /proc/cpuinfo
8

But running

#!java

public class ThreadUtils {
  public static void main(String[] args) {
    System.out.println("Number of available processors: " + Runtime.getRuntime().availableProcessors());
  }
}

produces a wrong result:

Number of available processors: 1

Running ThreadUtils on a local machine with the same docker image maven:3-jdk-11-slim produces the expected result of correct number of CPU cores.