Cannot insert custom block into ‘product.price.final’ in XML

Here is my catalog_product_view.xml:
I want to insert one CustomBlock to this final price block, so i can use getChildHtml() to call in template final_price.phtml, but it does not work so far, why ?

 <referenceBlock name="product.price.final">
        <block class="MagentoFrameworkViewElementTemplate" name="custom.block"  template="CustomModule::custom.phtml"/>
    </referenceBlock>