Send also to dblog

This is my service definition:

parameters:
  monolog.channel_handlers:
    default:
      - default_handler
      - drupal.dblog
  monolog.processors:
    - ...
    ...
services:
  monolog.handler.default_handler:
    class: Monolog\Handler\RotatingFileHandler
    arguments: ['/tmp/drupal.log', 10, '100']

With this setup, I'm expecting that log entries are recorded to /tmp/drupal.log (rotated) but also in the watchdog table. But watchdog is empty