Because, samui is a private airport owned by Bangkok airways. And you have to pay lots to use the runway.
@Flight-Reports2 ай бұрын
Samui Airport (USM) is owned by Bangkok Airways, so the price is very high compare to other domestic flights in Thailand. (*) Bangkok Airways also owns Sukhothai (THS) and Trat (TDX) airports, and, of course, the prices are very high also when you fly from/to these airports