1. Because they are much harder to make then Live2D one's, both the creation process of the model itself (sometimes taking up a month or more to create 1 model) and the rigging of the model to fit the facerig requirements (you can't just copy in a model and have it work, the bones need to have certain names so facerig knows that bone X is the neck and not the eye)
2. Because using "ripped models" is against copyright laws and are removed (same for 2D avatars, see the official statement here, which also talks about 3D avatars: https://steamhost.cn/steamcommunity_com/app/274920/discussions/8/487877107137546657/ )

Well that sucks. I hope a bunch of 3D models are made for Facerig in the future. Imagion if a bunch of people in the furry community started making base models for this.

Hi, there are a few 3D models on the workshop, you can find them here:
https://steamhost.cn/steamcommunity_com/workshop/discussions/18446744073709551615/133259956024920069/?appid=274920

And also there are these skins made by the community a while back:
https://facerig.com/news/community-made-textures-danny-taj/