This has happened to me twice coming out of Perth where the flight has been delayed overnight.
We had to reenter Oz again as we had been waiting to board both times.
We got a big blue stamp across the Oz departure stamp "Did Not Depart"
Got our passports back & taken by bus to accommodation.
Maybe Thai Immigration did not want the job of checking back in & out & making it quicker to get through & on their way when plane became available.
It would be Immigration that had the say, not the airline,,,, methinks