Drupal - Routing match everything

The reason that the route in system.routing.yml works is that it gets help by an inbound path processor service, which stores the filepath to a query parameter in the request:

PathProcessorFiles.php

<?php

namespace Drupal\system\PathProcessor;

use Drupal\Core\PathProcessor\InboundPathProcessorInterface;
use Symfony\Component\HttpFoundation\Request;

/**
 * Defines a path processor to rewrite file URLs.
 *
 * As the route system does not allow arbitrary amount of parameters convert
 * the file path to a query parameter on the request.
 */
class PathProcessorFiles implements InboundPathProcessorInterface {

  /**
   * {@inheritdoc}
   */
  public function processInbound($path, Request $request) {
    if (strpos($path, '/system/files/') === 0 && !$request->query->has('file')) {
      $file_path = preg_replace('|^\/system\/files\/|', '', $path);
      $request->query->set('file', $file_path);
      return '/system/files';
    }
    return $path;
  }

}

This service is registered in system.services.yml:

system.services.yml

  services:

    path_processor.files:
      class: Drupal\system\PathProcessor\PathProcessorFiles
      tags:
        - { name: path_processor_inbound, priority: 200 }

And the controller gets the file path from the query parameter added by the processor:

FileDownloadController.php

  public function download(Request $request, $scheme = 'private') {
    $target = $request->query->get('file');
    ...

You can implement the same approach for your route to match everything after /example/.