Drupal is an Enterprise CMS without corporate ownership
Drupal is a powerful force in the CMS market. While it dwarfs in comparison to WordPress, it is also a more comprehensive system that takes expertise to use. Especially in the recent iterations this Open Source Content Management System has increasingly targeted the Enterprise markets.
It is safe to say nowadays that Drupal is an Enterprise CMS. It powers billion dollar businesses sometimes in business critical tasks. This poses a problem when it comes to product ownership. As an independent project Drupal is vulnerable to changes in the free working force of the community.
While there are funded corporate entities like Acquia using Drupal as their core tool in their business, the investment does not go directly to the Open Source product (see Acquia vs. Drupal). This means that in the long term the tool might fare well, but no business has absolute control over it.
This leaves the Drupal project (and many other Open Source tools) vulnerable to community controversy, such as as the recent reports of the prominent Drupal core developer Larry Garfield being ousted from the project indicate.
In addition to social science a lack of distinct corporate control also leaves the project vulnerable to technical obsolescence. After having spent years reinventing core structures of the system with adopting Object Oriented PHP and Symfony Components.
While this was probably a necessary exercise to keep the projects back end architecture and security (a security flaw in Drupal played a part in the notorious Panama papers leak) relevant, the Drupal project as a whole has consistently failed to innovate in user experience.