▶️ Commercial is for merchandising
▶️ Monetized is any art used for your brand, whether it profits you directly or indirectly (Starting soon screen, streaming assets, etc)
The fact that you will not earn more from the hosting platform is unrelated, what matters is that this profits your brand, your image. Just like an ad does not guarantee extra sales, but will still benefit your brand.
▶️ Personnal use is basically collecting, sharing to friends, just enjoying the art for yourself.
When you're a VTuber, you might end up being charged a "Monetized license" extra, because if you end up posting it publicly it's now a part of your brand (unlike anyone's OC or fanart comm).
Some would argue it's unfair, personnaly if it's a small content creator or just social media purpose I wouldn't charge but it's up to each artist's preference.
➡️ To conclude:
- Milking any VTuber just because they're a VTuber isn't fair, and Monetized usage should only be charged fairly when applicable.
- Never charging Monetized usage isn't fair either as artists should be compensated fairly for promotional material.