This $date_field_array = get_field('event_the_date');
only gets a single value from a single post.
To get all values from all posts you first need to do a query to get all the posts, then you need to loop though all of those posts and get the field from each post.
$args = array(/* your query args here */);
$my_query = new WP_Query($args);
if ($my_query->have_posts()) {
$dates = array();
while (($my_query->have_posts()) {
$my_query->the_post();
$dates[] = get_field('event_the_date');
}
// output dates to JS here
}