Do most of us use avatars? I don't but perhaps less on principle than habit. I was old before computers made them possible.
A perhaps curmudgeonly observation is that Avatars extend adolescence, that marvelous age of experimentation, trying on roles.
Shy? Maybe, but a certain wariness of the astounding seductiveness of commercial and other propaganda is also wise. Then too, avatars may provide escape from the grindingly mundane. In that an alternative for alcohol and drugs. Avatars may useful or a distraction from coming to terms with ourselves.
I can't say Michael, you tell me?
As I'm sure you know, there are various reasons for wishing to protect one's privacy online. Even on Facebook, there are those who don't publish their own photos.
I haven't chosen an avatar yet. It might be fun.