I wondered that, too. It is strangely coincidental that ceasing to sell tickets for 2018 flights coincides with the US getting serious about sanctions. If sanctions caused it, you have to wonder why flights started the year Obama was elected and ended the year Trump took office.
Frankly, I don’t think there is any coincidence in the dates, nor do I doubt that Obama favored North Korea getting nuclear weapons. (As did Hillary and Kerry.)
I kid you not. I once heard a lib emphatically state they are “entitled” to them because we have them.