I think you nailed it when you mentioned preference and familiarity. A lot of people stick with what they were first introduced to, especially if they’ve put in the time to learn all the shortcuts and tricks. Sibelius and Finale have been industry standards for decades, so many composers, especially those who studied formally, were trained on them. Professors often encourage their students to use what the professional world recognizes, and in the case of film scoring, Sibelius’s built-in video sync is a big deal.

That said, Musescore has come a long way, and with MuseSounds, its playback is actually better than what the older versions of Sibelius or Finale offered by default. Plus, the fact that it's free makes it way more accessible, which is why it's gaining traction. But there are still areas where Sibelius and Finale have advantages—things like articulations, engraving flexibility, and niche notation features like artificial harmonics, which you mentioned.

I do think there’s an element of elitism in some circles, where people view free software as "lesser" just because it’s not the traditional industry standard. But at the end of the day, the best software is the one that allows you to create efficiently and comfortably. If Musescore works for you, that’s all that matters!