Actually the main reason why we had the airports in both CM & Phuket connect to BKK is because 1) i would say about at least 95% of flights from CM to Phuket or from Phuket to CM actually do connect to BKK first and 2) To show the dominance of Bangkok for what it really is... BKK runs Thailand and ...
I think this should be a map-specific option...like the opposite of bombardment options on some maps. Instead of two unconnected territories being able to attack one another, they can reinforce one another.
But I think this option might already be in place?...