Custom Articles page only showing a limited number of posts per page

The post limit is controlled in the admin panel, at Settings > Reading. There you can set the limit for how many posts should be shown in a query. However, the default post count for get_posts() is 5.

If you would like to query unlimited posts (regardless of performance issues), you can either create your own instance of WP_Query() or use the pre_get_posts filter to do so.

Using WP_Query() is pretty straight forward, and all you have to do is to pass -1 to the query. You can do the same with get_posts() :

$args = array (
    'posts_per_page' => -1,
    // Rest of the arguments here
);

$query = new WP_Query($args);

Now you can use a simple while() loop to output your content.