I only build Drupal websites and here's why:
Drupal's content management framework is incredibly versatile, robust, scalable, and wildly extendable. Looking at my decision to use Drupal from a programming and extendability perspective, Drupal's flexibility is nirvana. Unlike some other CSMs like Wordpress or Joomla, there are NO limitations with Drupal.
Add to that, an amazing and thriving community of developers and users and I've got everything I need to build and support websites of all sizes for any industry.
Drupal allows me to build anything from small, five-page sites to large, information-heavy sites... and everything in between.
Here are just a few of the many organizations that are using Drupal today:
As you can see, you will be in good company.