Posting the question here at your forum, and not the Drupal forum. The standaard reply on a Drupal forum would be: because we are more flexible, powerful, extensible... because we're sort of a framework and not a...
But I wonder what the Omeka community thinks about it all. Apologies in advance for a rather lengthy post.
A bit more specific pro's for both:
- Dublin core is in both
- OAI PMH is in both
Pro's for Omeka:
- Works out of the box
- Specifically tailored for collections
Pro's for Drupal:
- Huge community and plenty of developers anywhere in the world
- Any metadata can be added to Drupal
- A huge amount of modules
- lots of third party integrations
- Easily create multisites
- Building collections is rather easy through content types and views
What I don't know:
- Are files organized in a specific folder structure
- Can I add files to a folder through FTP and add them as such to Omeka?
More specific questions:
- Why did the developers decided to build another CMS and not simply build packages for Drupal?
- What is possible in Omeka and not in Drupal?