Drupal uses a ton of RAM and is super inefficient. While you're installing new versions each time you upgrade, all those new versions are built on top of the existing code. Eight generations in and the mess of Drupal's backlog is beginning to cause it to collapse under its own weight.

Not Good for Non-Technical Users

This presents issues for non-technical users who might not be able to use Drupal to its maximum potential. Plus, on Drupal, it's expensive to develop yourself, meaning that you may not always be able to take advantage of new features that competitors are adopting in this situation.