Avatar is used synonymously with profile picture. If I said I had an "avatar," the last thing you would think of is a fully rigged and mocapped 2d/3d avatar. Notice how I had to qualify the word avatar there ("animated avatar" is hardly specific enough), hence why it has its own name: vtuber.
Get over it. You keep complaining about the word vtuber in this thread, but it's an extremely common and popular term with a whole damn industry behind it.
The term virtual youtuber comes from japanese for what it's worth. It's a loan word of a loan word. It's the term that is used.
And avatar is used in the space. They are "formally" called vtuber avatars or vtuber models. But the occupation/hobby is called vtubing and a person who uses them is a vtuber.
It's not that avatar isn't used. It's just not specific enough to what this is. vtubing rigs specifically aren't exactly general purpose. Some of them are and work as avatars that can be used with mocap or vrchat or whatever but a lot of them just aren't. A lot of them are "Live2D" which is a much more restricted type of model that is effectively various different transform and distortion effects on 2d images to give the perception of 3d motion.
Avatar covers a lot of things. Vtubers are a very specific subculture. They have avatars/models but to just call them avatars sells them quite a bit short of what they are specifically.
This comment, and the fact that you had to make this point twice (three times actually!) in this thread, is some real "old man yells at cloud" energy.
There is nuance to the term that "avatar" doesn't remotely capture. Language is ever-evolving. Keep up with the times, or ignore it. But yelling about going backwards is a waste for you to type and a waste for everyone to read.
Get over it. You keep complaining about the word vtuber in this thread, but it's an extremely common and popular term with a whole damn industry behind it.