read_triangle_model --- read_triangle_mesh not compatible

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### Describe the issue

When using each of the methods
1. read_triangle_model
2. read_triangle_mesh

To load the same glb file, I am getting different number of vertices.

Is this a desired discrepancy?

### Steps to reproduce the bug

```python
import open3d as o3d

model_file = "model.glb"
mesh_model = o3d.io.read_triangle_model(model_file)
mesh_0 = mesh_model.meshes[0].mesh
mesh_1 = o3d.io.read_triangle_mesh(model_file)

len(mesh1.vertices) == len(mesh0.vertices)
```

### Error message

False

### Expected behavior

Expect the number of vertices to be the same.

### Open3D, Python and System information

```markdown
- Operating system: macOS 12.6.2
- Python version: Python 3.9
- Open3D version: output from python: 0.16.1
- Is this a remote workstation?: no
- How did you install Open3D?: pip
```

### Additional information

_No response_