Hi, thanks for your answer!
But considering the quality, the relentless development and support, and the willingness to consider, evaluate and implement pretty much every single sensible request or proposal from users, I find it a bit inappropriate and maybe even disrespectful to the developer to suggest that MusicBee should better be open-source.
I don't agree with that. I didn't say MusicBee isn't well-developed or that the development is slow in any way. What I said is that open-sourcing the project would allow other people to contribute and implement many features the current maintainer may not have the time to. Look at big open-source projects, they usually benefit from the participation of external persons as it allows to fasten up the development.
Of course open-sourcing MusicBee isn't required ; there isn't security concerns in a music player, and the software is almost bug-free (which is quite incredible given its complexity and the fact it's only maintained by a single develop, by the way).
As for the examples you give:
Would you ask a musician why his work isn't open-source so that other people can work on his compositions and so improve his music?
Composing a music is very difficult to do if you're not alone, as it's not something as "mathematical" (I don't have a better word here) as software development.
Or the writer of a book, or an architect who is building a house?
A book writer or an architect sell what they produce, which isn't the case of MusicBee and as I understood there is no plan to making this paid in the future. If it is, please correct me and of course it would completely make sense in that case that the source code isn't public.
On the other hand, open-sourcing this project would also simplify development of third-party tools, be it completely external programs or plugins.
Also, don't forget it's possible to use a license that doesn't allow other persons to re-use the project's code without the author's permission, or even to distribute it without permission.
I absolutely don't think it's a problem for MusicBee to not be open-source, I simply don't understand the reasons why it isn't currently. I'm sure the current maintainer has reasons, which is why I'm asking what they are as I think I'm not the only person wondering why this software is closed-source

If you have coding talents and are not satisfied with the current lyrics features, take a look here:
https://getmusicbee.com/forum/index.php?topic=25406.0
Perhaps you can contribute to MusicBee by helping to further improve that plugin?
I'm already digging into this plugin's code, I was just giving an example

But I think it would also be great to have this kind of feature implemented directly in MusicBee. It would take a bit of time to implement this inside the current software, which is where open-sourcing it would be a perfect example of usefulness: other devs could make the changes to the current project and the maintainer could review them and accept or reject them based on if they think the changes are relevant or not
