Singapore airlines get access to a lot of the best long haul routes in the world because its government negotiates it for them as part of larger trade deals.

Singapore is also well situated politically (it has no real enemies anymore, so while China may deny a US airline they wouldn't deny Singapore), geographically and commercially in terms of global trade.

The lesson here is that if you want to run a super cheap airline, make sure you are backed by the government of one of the wealthiest countries and major trading hubs in the world.

Yes, it's kind of like comparing a state owned oil company to Exxon. Another example is Emirates. Can't blame the govt for backing the airline, though, as it leverages a huge strength: Dubai is within 1 stop of virtually all airports in the world.