Airflow DAG Run triggered, but never executed?

The accepted answer is correct. This issue can be handled through UI.

One other way of handling this is by using configuration.

By defualt all dags are paused on creation. You can check the default configuration in airflow.cfg

# Are DAGs paused by default at creation
dags_are_paused_at_creation = True

Turning the flag on will start your dag after the next heartbeat.

Relevant git issue

The problem is that the dag is paused.

In the screenshot you have provided, in the top left corner, flip this to On and that should do it.

This is a common "gotcha" when starting out with airflow.