user roles – Why does current_user_can(‘edit_posts’) return true, but current_user_can(‘edit_post’, $post->ID) return false?

I have a plugin with a custom post type (with 'capability_type' => 'post') and a custom user role (test_user). When I check if a user is allowed to edit a post (of the CPT and which this user created) with current_user_can, I get different results when using edit_post and edit_posts (with the s).

See example code below:

register_post_type('test_cpt', (
        'labels'             => ('name' => 'TEST CPT'),
        'description'        => 'A custom post type for testing',
        'public'             => true,
        'publicly_queryable' => true,
        'show_ui'            => true,
        'show_in_menu'       => true,
        'query_var'          => true,
        'rewrite'            => ('slug' => 'testcpt'),
        'capability_type'    => 'post',
        'has_archive'        => true,
        'hierarchical'       => false,

$new_post = (
    'post_content' => 'Lorem ipsum dolor sit amet consectetur adipisicing elit.',
    'post_name' => 'test',
    'post_title' => 'TEST',
    'post_status' => 'publish',
    'post_type' => 'test_cpt'
$new_post = (
    'post_content' => 'Lorem ipsum dolor sit amet consectetur adipisicing elit.',
    'post_name' => 'test_post',
    'post_title' => 'TEST post',
    'post_status' => 'publish',
    'post_type' => 'post'

$user_id = get_current_user_id();
$data = get_userdata( $user_id );
echo '<pre>' . print_r( $data->allcaps, true ) . '</pre>';

$id = 153;
$post = get_post( $id ); 
echo '<dl>';

echo '<dt>current user: </dt>';
echo '<dd>'. $user_id . '</dd>';

echo '<dt>post id: </dt>';
echo '<dd>'. $post->ID . '</dd>';

echo '<dt>post_author: </dt>';
echo '<dd>'. $post->post_author . '</dd>';

echo '<dt>edit_posts: </dt>';
echo '<dd>'. (current_user_can('edit_posts') ? 'true' : 'false') . '</dd>';

echo '<dt>edit_post '.$post->ID.': </dt>';
echo '<dd>'. (current_user_can('edit_post', $post->ID) ? 'true' : 'false') . '</dd>';

echo '</dl>';

which results to:

    (read) => 1
    (edit_posts) => 1
    (upload_files) => 1
    (test_user) => 1

current user:     3
post id:          153
post_author:      3
edit_posts:       true
edit_post 153:    false

According to this post edit_post evaluates to the capability edit_posts if the post_author field of this post matches the current users ID. Which makes sense and what I expected.

If I include the code provided in this WP SE answer, then I also get true for edit_post.

But I do not understand why this is necessary. It seems to me, that there should be a better way to deal with this situation. I would image this is a pretty common use case.