Classic themes require header.php and footer.php files that include essential WordPress functions like wp_head(), wp_footer(), and wp_body_open(). These files output the complete HTML structure from doctype to closing tags.
Block themes simplify this dramatically. Header and footer template parts contain only the presentational content – WordPress handles all the technical HTML structure, head content, and hook calls automatically.
In classic themes, templates represent entire pages. In block themes, templates only define the content area within the wp-site-blocks container. WordPress generates everything else.
This simplification lets developers focus on design and functionality rather than memorizing WordPress conventions and hook requirements. Block theme template parts are purely presentational without technical overhead.