It might be somewhere, but I don't think it makes sense because:
First, if the centralized wallet is set to open source, it will open its own security vulnerabilities to a certain extent. The data displayed on the application is reflected from their servers which can generally be hacked, or even abuse the application system without touching the server at all.
Second, usually they will protect the code from plagiarism especially from competitors. They simply gave a "copyright" reason.