I understand your point XD but want to emphasize, software is NOT like tangible items, and any analogy to them will fall flat.
Giving out the source code to an abandoned application does not mean the original owner doesn't still have their copy.
By just dumping the code online, the software has the potential to be worked on by other people. This can benefit everyone, including the original developer.
Even so, there's plenty of valid reasons to not do it. Licensing issues (did anyone else work on any part of the project using a different license?), pride (no longer being the "owner"), getting it online (choosing a license, getting it online, it all takes at least some time and effort), or just plain "I don't want to" are all valid reasons.
I have projects. Games that were in the google play store. One had hundreds of thousands of downloads. Then Google pulled it as I didn't maintain it. But, I have to pull artwork out, sound effects, etc that can not be included. And that's just time. I don't have much of that, that's due sure.
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.
It's a whole licensing thing where they have very little to gain but a lot to lose. Intelectual property is very important in the IT world, companies tend to keep their work for themselves.
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
I remember the news when Dwango company decided to open source the Toonz program.
On one of the forums I read a lot of criticism about the quality of their code.
But no one will deny that this is a useful program for artists, even if the program code is not very good.
@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.
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.
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.
Maybe you could find some answers if you have a look into apps that actually did what you suggest and see how they did through time. Comes to my mind, for example, Astrid, a to-do app that became FOSS after a good run in the early android days.