There are many closed source applications that have been removed from the Google Play catalog for various reasons.
Often this reason is the cessation of further development and maintenance of the application.
Why don't these people make the code open to everyone if they don't need it anymore?
This could bring great benefits to all people, but everything that was once created simply disappears.
@Slow It's most likely due to they rather delete there files before they think "Oh, I can just release this on GitHub or something Publicly for people to use my code" or due to being apart of a company that is very protective of its property or it's due to feeling they may come back to the project in the future and improve it.