The name of the project made me think of the infamous DB Cooper and so the sheep follows the FBI wanted poster.
TL;DR Our internal, confidential, tools are based off of the code that we open source. This means that they are a derivative of any source in those projects, so if we'd like to continue sharing our source and developing on top of it, we need a license that allows us to do so.
More Details DB Shepherd is open source, development is done in public view, and we don't intend to change that. Even if we did, however, rest assured that DB Shepherd will always remain open source (you can't unlicense open source, the original license remains in effect for anyone who has a copy, this is how projects like MariaDB continue to function after Oracle purchased MySQL AB).
For our uses, however, we can't continue to build our own internal tools based off of our open source code unless we have the legal right to do so. If we own the copyright, that's easy, we have that choice. If we don't, however, we need permission to create derivative works. Without that, we'd have to maintain two versions, one that contained purely code that we wrote, and one that might contain contributions we don't have the right to use. In addition to being extra work for everyone involved, it's needlessly confusing for any users.
That's why we ask for a CLA. With a Contributor License Agreement, you grant a license to us for any contributions you make. You still own the copyright to your own code, so you can make contributions, use the exact same code at home, publish a book, even sell off your future copyright.
We, however, also have a right to use those contributions in a manner similar to having a copyright. We can build on top of these contributions, even for our internal tools, and continue releasing our improvements under an open source license.
We think this strikes a fair balance between all of the parties involved. We can open source the work we want to, and feel comfortable engaging the community and any contributions they make. You can benefit from any changes you contribute, and even use those changes however you see fit, and users can benefit from all contributions without having to worry about think about the licensing structure if they don't want to.