If you use many themes or have large files, Joomla can become very CPU-intensive. Additionally, if you're using many plugins, Joomla can slow down your website. One of the most significant disadvantages of using Joomla for your website is using paid plugins.

You have to pay, WordPress has more free plugins and Themes, and this is also true for Drupal. But for Drupal you have to know more about Web Dev.

Joomla can place many demands on your server resources, depending on the number of pages you create, the size of your images, and the number of themes you use. If you use many themes or have large files, Joomla can become very CPU-intensive. Additionally, if you're using many plugins, Joomla can slow down your website.