Comment by KeePassium

Yes, you got it right. The source code is published under the GPL, but App Store ToS impose additional restrictions that are incompatible with the GPL. So we have to dual-license the project, and only the copyright owner can do that. In order to maintain that role, we can only accept contributions with a CLA (two pages of legalese that transfer the copyright). This is obviously a deterrent for contributions: over the 5 years, I believe there were only 3 people who signed it :)