specialize function when using custom vertex attributes

[jonathandw743]

Why is this not the default implementation?
is there something i am missing here?

fn specialize(
    descriptor: &mut bevy::render::render_resource::RenderPipelineDescriptor,
    layout: &bevy::render::mesh::MeshVertexBufferLayoutRef,
    _key: bevy::sprite::Material2dKey<Self>,
) -> Result<(), bevy::render::render_resource::SpecializedMeshPipelineError> {
    descriptor.vertex.buffers = vec![layout.0.layout().clone()];
    Ok(())
}