Essentially every single airport in the world is custom UI and custom walking path guides and pickup instructions, and rules for where pickups/dropoffs/etc can occur can change multiple times in a day, much to everyone's enjoyment. They're almost all private property, and are so valuable that whatever they want is what they get.
And food. Most/~all? major brands get custom integrations.
Hundreds (iirc) of identity verification providers, most or all custom, and constantly weighed against cost and accuracy because it ain't cheap and it ain't good but it is far better than none (both legally and ethically).
No idea how many payment sources they accept, but it's definitely a lot more than anyone who hasn't lived on 5+ continents thinks.
And remember that this is all international. So scale is huge and law changes are constant and frequently conflicting. Darn near every useful feature is illegal somewhere, at some time, for both good and bad reasons.
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This is not at all to say I think Uber is efficient, clearly it is not. Not by an enormous margin. But there is a legitimate need for truly absurd complexity, because the world is not consistent. You see similar things happen anywhere [thing] tightly interacts with humans.