More and more, publishers depend on the authors to sell their own books. If they feel really strongly about a property, they might add advertising bucks behind it, but you can't count on that.
What can be enticing about the traditional path is the advance on royalties. This is a guaranteed, up-front payment for your work that will be taken out of royalties if your book sells. Once enough copies are sold, you can then start to earn new royalties.
The publisher also has established channels of distribution that can open doors to book stores and other outlets. Depending on the publisher, it might also determine how much shelf space is given to your book.