Since the new Kunming airport opened, demand has dropped significantly. Most routes that I had double daily 737s on at ZPPP are now getting oversupply warnings at ZPPK. I checked demand and what was over 350 pax at ZPPP are now below 70 pax at ZPPK. This makes no sense as the new airport replaced the old one, it was not opened as a second airport in the city.
I did a search and it appears this has come up in previous games without an actual answer, just "yeah, that happened in MT4 too". So how is it that the new airport has 1/5th the demand of the old one, when the old airport is now closed?