It's kind of not relevant to my involvement with LilyPond since I've been its project lead for the better part of the last 1½ decades. Its popularity is more related to a state of mind than the place of residence.
Well, if Free Software breaks, you get to keep the pieces. With proprietary software, you don't get to keep the pieces. But they have dedicated personnel shielding the developers from the users and making the users feel better about being without recourse. When the developer does not have the problematic gear at hand with Free Software, it falls to the user to do the experiments or donate hardware, and sometimes to give reminders.
The "Denemo developers" is mainly just Richard Shann, and Denemo is a separate project from LilyPond (which does right now have several active developers). The generally accepted best IDE for LilyPond these days is
Frescobaldi, an editing environment created in the context of the current
protestant songbook in the Netherlands entered by dozens of volunteers. You wouldn't know from the website these days, but it has been created using LilyPond. As opposed to Denemo, you don't manipulate notes graphically in Frescobaldi but do get reasonably fast graphical feedback.
Frescobaldi has MIDI entry of notes but that is nothing to write home about in my opinion. If you are good at rhythmical play, it probably makes more sense to play your content into Rosegarden, a MIDI synthesizer that is able to do quantization, and then export your content as a LilyPond file.
In the end, I find that just biting the bullet and entering in LilyPond's native language with a typewriter keyboard is the most unproblematic manner of working, and Frescobaldi does a good job supporting that.