Asia often doesn't have any infrastructure in place of air travel. The US and Europe have large roadways and rail networks for transportation which means airfare is more expensive in relation. Much of Asia has no road or rail network in place that can support the capacity that air travel offers and many governments in Asia cannot fund a road or rail project of sufficient magnitude to offer a compelling alternative. In Europe jet fuel is mostly untaxed and distances in Europe are shorter so less fuel is spent moving passengers from city-to-city.

EasyJet from Dublin to Milan is so cheap, as are international flights like KL to Taiwan These are distances that aren’t feasible to drive even if they were on the same landmass.

And as you say europe also has a dense road network. The fuel tax is interesting, definitely, but in my US/EU comparison price delta is often a factor of five or more.

Flights between KL and Taiwan are cheaper because labor and maintenance is cheap thanks to the much lower wages in KL and Taiwan compared to Europe and the US (so everything from maintenance to refueling is cheaper).

As far as taxes are concerned, it would be interesting to do a cost breakdown of fuel to see how much of the delta comes from taxes.