Many stopped cause they don't have a product that can keep users. A signature campaign can only attract potential users to click on the link and check out the site, what they find there will determine if they will be users or one-time visitors.

Brand building is a holistic approach which is why a review campaign along with a signature campaign is always a good idea to get a feel of what the community wants and what fixes they should make on their site, not every business is ready to build a brand.