but, if it’s not so difficult, why don’t you think about implementing it in your plugin, and also…
Because there are, literally, hundreds of requests like yours. I don’t have the time or energy to do everybody else’s work for them; I just built the plugin that I needed, and then put it out there for others to use if it fit their needs too. Along the way I have put a lot of extra work into it to make it more useful for others, but there are limits.
I think users will be happy to pay for such a plugin,
I don’t have any interest in making money off my plugins. Even if I did, it’s not a particularly attractive business model; there are very few people who can actually make a decent living doing it.