Always On Availability Group ApplicationIntent=ReadOnly Not routing to Secondary
You have to have a read-routing list, even with only two instances, if you want to offload reads to a secondary replica. 

The following script is an example of setting this up (you would change the AG name to whatever your AG is, and the replicas to your servernames (using the fully qualified domain name, and adjusting the port if required).

ALTER AVAILABILITY GROUP YOURAGNAME MODIFY REPLICA ON 'REPLICA1' with (SECONDARY_ROLE (READ_ONLY_ROUTING_URL = N'TCP://REPLICA1.FQDN:1433'));
ALTER AVAILABILITY GROUP YOURAGNAME MODIFY REPLICA ON 'REPLICA2' with (SECONDARY_ROLE (READ_ONLY_ROUTING_URL = N'TCP://REPLICA2.FQDN:1433'));

ALTER AVAILABILITY GROUP YOURAGNAME MODIFY REPLICA ON 'REPLICA1' with (PRIMARY_ROLE (READ_ONLY_ROUTING_LIST = ('REPLICA2', 'REPLICA1')));
ALTER AVAILABILITY GROUP YOURAGNAME MODIFY REPLICA ON 'REPLICA2' with (PRIMARY_ROLE (READ_ONLY_ROUTING_LIST = ('REPLICA1', 'REPLICA2')));


As regards the flags:


ReadIntent allows for connections only passed along with the
ApplicationIntent=ReadOnly flag  
Yes allows for any connection to the
database (meaning you could connect directly with SSMS and run
queries)