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.
Because I don’t want people seeing my terrible code
It’s probably unmaintained because they don’t care any more, or don’t have the time. If they don’t care or have time, they are not going to spend the effort and time required to open source it and publicise that fact
In addition to other reasons already given, commercial software may contain licensed code, libraries, assets, trademarks, and other IP that cannot legally be given away for free, or under an open source licence.
Sure, it may be possible to strip those things out, but that may leave the software broken or fundamentally changed, and it may be a significant amount of work to do, which am author or publisher is not likely to spend on abandoned software, especially if their free release would compete with any current products.
Additional question: wouldn’t it be cool to have a place where you can only get open source stuff? Obviously there needs to be more to it than this fact i presume but its a start.
F-Droid isn’t the only one: I also like Neo Store, which has more than just the F-Droid repository and I think has a better interface. However, I think not all repo are 100% safe because F-Droid verify all the apps they have while Neo-Store doesn’t because it simply list known repos, which you can activate however you like in the settings.