Upvote:1
As someone already suggested that's the market. I would advise to check flights from Bangkok, KL or Singapore to USA and find if those are cheaper and then book cheap flight from VN to those destinations.
Upvote:21
Flights are priced based on market, not particularly distance flown. So frequently prices going one way can be different than the reverse route. Likewise the number of fare classes (fare buckets) can be different, so the jump between fares can be greater.
Though, I find the opposite of you for flights I deal with (Thailand-USA and China-USA) as round trips fares from Asia side seem to be lower than from the USA side.
As a general rule of thumb with airfares, forget any logic, it is purely market driven pricing.