"Goes down" could include things like "we're going to increase your pricing by 10 cents per charge". It's a much stronger negotiating position that Uber is in if they can say "we can switch 100% of our volume to Stripe in a minute by going to admin.uber.com and flipping a single feature flag".

Or even better: "we automatically route traffic to the cheaper option and this requires no human intervention, so don't even bother"

Large companies typically do payments in batches, not one-by-one, so the redundancy is not needed.

However, if they're trying to do per ride auths, then they might need redundancy there. Hard to imagine they do that.

I don't think they auth per ride. I definitely had a "you owe us money" flow after getting food successfully delivered though Uber eats on a deactivated card.

I get push notifications on auth on both my debit and credit cards. Weak evidence, but my hunch based on what I see there is that there's some dollar value where they pre-auth (somewhere around $25, I think).