Pipeline with Matrix doesn't see variables outside pipeline block

#!/usr/bin/env groovy

//library("jenkins_shared_library@1.0.0")

//@groovy.transform.Field
String resourcePrefix = new Date().getTime().toString()

//@groovy.transform.Field
Map dockerParameters = [
    registry: "docker.example.com",
    registryType: "internal",
    images: [
        image1: [image: "image1", dockerfile: "Dockerfile1"],
        image2: [image: "image2", dockerfile: "Dockerfile2"]
    ]
]

pipeline {
  agent any
  options { skipDefaultCheckout true }
  parameters {
    booleanParam defaultValue: true, description: 'Build & Push image1', name: 'image1'
    booleanParam defaultValue: true, description: 'Build & Push image2', name: 'image2'
  }

  stages {
    stage("Prepare") {
      options { skipDefaultCheckout true }
      failFast true
      parallel {
        stage('Test1') {
          steps {
            // All variables available in simple stages and parallel blocks
            echo "resourcePrefix: ${resourcePrefix}"
            echo "dockerParameters: ${dockerParameters}"
          }
        }
        stage('Test2') {
          steps {
            echo "resourcePrefix: ${resourcePrefix}"
            echo "dockerParameters: ${dockerParameters}"
          }
        }
      }
    }


    stage("Docker") {
      options { skipDefaultCheckout true }
      matrix {
        axes {
          axis {
            name 'COMPONENT'
            // Note: these values are the same as described in dockerParameters and params
            values 'image1', 'image2'
          }
        }
        stages {
          stage("Build") {
            when {
              beforeAgent true
              expression { params[COMPONENT] == true }
            }
            // agent { kubernetes(k8sAgent(name: 'dind')) }
            steps {
              // Failing on resourcePrefix/dockerParameters, as it doesn't have Field annotation
              // Question is: why variables are not available inside matrix?

              echo "resourcePrefix: ${resourcePrefix}"
              echo "dockerParameters: ${dockerParameters}"

              // Here is one step as example:
              //dockerBuild(
              //    image: dockerParameters.images[COMPONENT].image,
              //    dockerfile: dockerParameters.images[COMPONENT].dockerfile
              //)
            }
          }
        }
      }
    }

  }
}

groovy.lang.MissingPropertyException: No such property: resourcePrefix for class: groovy.lang.Binding