They would be interested in your data because the more they have the more subscribers who will pay the price to see it. Ancestry.com is a prime example. Though the information on Census records and other public data is not copyrighted, users by the millions pay for access to the database as it represents an easier way to find and view family records.
The more data the more valuable, including yours. No matter how good the software if it did not contain sufficient data to include as many families as possible people would not pay to see what would be limited information.