Grunt imagemin not optimizing, what could be the problem?

Question

Grunt.js

I apologize right away for the imperfect look of the Grunfile.js code:
we have such a code and different photos distributed in the images folder

module.exports = function(grunt) { 

grunt.initConfig({
 imagemin: { 
       images: { 
             options: { 
                optimizationLevel: 3 
              }, 

            files: [{ 
                expand: true, 
                 src: ["images/**/*.{png,jpg,gif,svg}"] 
             }] 
         } 
      }
 });

grunt.loadNpmTasks('grunt-contrib-imagemin');
grunt.registerTask('default', ['imagemin']);

};

when running in the console, we get:
Running "imagemin:images" (imagemin) task
but no optimizations occur ((what could be wrong??