Part of this has a decent reason: If fuel is much cheaper in e.g. Dubai, airlines will chock their planes full of fuel instead of the optimised amount, leading to overburning of fuel due to excessive transportation of it.

And the opposite, they will skimp on fuel going inbound to there. Of course fuel qty is the captain's decision, however a lot of airlines already pressure those. As one example Ryanair had a "list of shame" of captains bringing too much safety fuel in their eyes.