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.
XNViewMP… the dev is basically gone, but they are opposed to OpenSource. XNViewMP is even a QT showcase project, and with opensourcing its features could be easily split up, converted, UI modernized, Wayland adapted etc. Its easier and faster than GIMP, especially for batch image converting and all that. Its great software.