Drupal has one of biggest and more active communities across FOSS, maintaining a large and vibrant ecosystem of extensions and installation profiles. The large community makes it easy to get help when needed.
Drupal can be customized to do almost anything. It was built ground up with the intent of using a wide variety of small modules to get the exact result wanted instead of just the most common solutions.
Drupal is an advanced CMS that requires developer expertise. If you do not have someone on your team with developer experience, Drupal may not be the CMS for you.
Drupal is not easy to get into and out of the box doesn't offer much. To get Drupal doing what you want it to, modules are required. To get modules, an understanding of how Drupal works is required. And that takes time.