Get all woocommerce comments/reviews

Please try this:

 $args = array( 
                'number'      => 100, 
                'status'      => 'approve', 
                'post_status' => 'publish', 
                'post_type'   => 'product' 
        );

 $comments = get_comments( $args );

where you can edit the number of comments to your needs.

Debug:

Maybe something is changing it via the pre_get_comments hook?

To debug it you can check out the SQL query with:

 global $wpdb;
 printf( '<pre>%s</pre>', $wpdb->last_query );

where you add this directly below the above get_comments() code snippet.

Also check the edit-comments.php screen if the comments show up there and their status.