Airlines use a complex algorithm for booking flights, here are some of the considerations: Shorter direct flights tend to be more expensive, day time flight more expensive. Some routes Monday and Friday are more expensive because they attract business travel, some airlines give a basic price and then offer upgrades for flexibility, seat allocation and baggage. If the flight is nearly fall the price will rise. In the case you shown I suspect its due the higher price being business.
DDP means the supplier covers all costs of delivery and tax, I have never seen any mention of it on any lazada store. They all seem only to have a nominal delivery charge, probably less than if you were to ship internally in Thailand. Hence my question.