Archive template for custom post type only lists first 10

In function.php

add_action('pre_get_posts','show_all_people');

function show_all_people( $query ) {
  if ( $query->is_main_query() && is_post_type_archive('people') ) {
    $query->set('posts_per_page', -1);
  }
}

See Codex docs for pre_get_posts hook