Technically,
Contract of carriage ties everything to scheduled departure time. Not sure the specific on WN based on a cursory glance through the CoC but just about every airline has a disclaimer that despite any sort of posted delay, it is still the customer's responsibility to check in and be available to travel based on the original scheduled departure time.

Yes, it can get a little ridiculous. Do they really expect you to be there at noon when they've just told you the flight is delayed until 8pm? That's debatable, but it could always pop back up on time. In my days as an airline manager, I had to go to court on behalf of my employer at least twice I can recall due to customers suing the airline over missing a flight because a delay disappeared. Lost one because the judge just couldn't believe that a delayed flight somehow departed on time (had outlined it was at a hub airport, three way aircraft swap matched up a broken plane with a flight that was on a lengthy weather delay and put two other flights back to or close to on time). Won the other because the plaintiff/customer's own exhibit showed the line at the bottom of the notification to still be at the airport on time.

Probably not worth complaining. At least with WN you were able to salvage the value/move the flight. At many other carriers you would have paid a penalty or forfeited for missing your flight.