Drupal's user and developer base

Drupal is used by tens of thousands of sites on the web, and more than seven hundred people are visiting drupal.org as I write this. This gives you several advantages if you take the Drupal path:

• Modules for a wide range of needs: As you build your site, needs may arise which you didn't predict. As users of Drupal experience needs, a module is often written to fill it. In most cases these are contributed, so with the Drupal path you have the opportunity to download modules and easily plug these into a system which is able to handle them. Furthermore, you have the opportunity to hack the modules to fit your needs better as they are open source.
• Easy access to help: As mentioned, lots of people are active on drupal.org. Letting them know of your problems in the forum or searching there will often result in suggested solutions. When rolling your own system, you don't have the advantage of a large community "speaking the language" of your framework.
• A thoroughly tested platform: As the complexity of a system grows, it is likely to create errors or bugs. It will eventually be difficult, if not impossible for mere human to predict all eventualities. You can not count on your site's visitors to report errors, because instead of reporting they may choose to leave.
  

  Every installed Drupal site comes with a watchdog module. This module logs errors and report them to the administrator when she visits the administation section of her site. Furthermore it is important for all users of Drupal that their sites work as expected. Therefore users report errors to the maintainers of Drupal and her modules. To ease this process, Drupal's maintainers have created a system which keeps track of issues, showing them to interested persons able to correct them.