Get used to it. Vast majority of days it's so. DL seems to have some major blocking of HA in place. On HA on virtually every day there are some award flights at the low mileage (7500 one way in case of HA), though usually just 5am, 6am and 10pm, 11pm departures. On DL you can sometimes may be get it one way, but then nothing return, even for multiple weeks in a row... either major intentional blocking of HA (to make it essentially impossible to get such an award flight), or just DulltaMatic being its usual buggy and useless self.