The problem is that Southwest does not operate red eye flights.
So for example, the earliest HNL/LAS flight gets into LAS at 4:45 pm. Allow 45 minutes for connections and the earliest you could leave LAS is 5:30 PM (8:30 ET). If you could hook on to a non stop flight you would get into ECP at 2:30AM the next day. If no non stop, but direct, it's even later. If you need a connection, you are not going to find one getting into ECP (or any other east coast airport) at 3 AM or later.
The reason you can find flights to Hawaii is that time zones help you. The reason you can't find flights back is that time zones hurt you. Now if SW were to offer 1 am departures from Hawaii, this would be easy, but it does not.
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