From Google:
A custom CMS is developed specifically for a business’s unique needs, offering complete control and customization, while a popular CMS is a pre-built platform like WordPress, offering ease of use and a wide range of features. Custom CMS provides the most flexibility, but comes at a higher cost and development time, while popular CMSs are more cost-effective and quicker to implement but offer less customization.
- bigger cost
- more time
- Maybe better quality
- faster site
- and more
- Managed site
- Use of a popular CMS like WordPress, Joomla, or Drupal
- Buy ready plugins/extensions/themes (low cost).
- or pay to create tailored plugins/extensions/themes (higher cost)
- and more
In any case, it is a balance of the time that you need to learn/create the software AND the cost that you have to pay in order to make the site if you use a popular CMS.
There is also the case to use a popular CMS (WordPress, Joomla, Drupal) and to develop plugins and themes; this is a middle solution.
To write no matter the cost/time is more the work of someone who likes to have a hobby.