Because there are no variations available for composite products. Sorry to say there are no options in theme settings to make like this in the composite product because it is coming from an external plugin. It requires customizations and this is beyond our limitations and support policy.
It is simply a drop-down menu and not thumbnails. This is what I am trying to change.
WooCommerce customer support wrote to me: In this case, it looks like your theme disables Variation Swatches within Composite Products. I recommend reaching out to your theme author.
Our theme does not contain code that would disable swatches in specific places. Composite Products cannot have swatches from our theme because our swatches are designed only for Variable products.
We haven’t tested this plugin with our theme, but if WooCommerce recommended it and it works with the default WooCommerce theme like Storefront, it should work with our theme as well.