Uber is betting that people don't realize 70 * 0.25 = 17.5

Or it's just deceptive marketing.

99% off a $100+ order! (capped at $10).

It might be just an example of Hanlon's razor since 25% is close enough to the effective 21% max off (if you spend exactly $70). But really this is a "$15 off orders >$70" discount.

From my personal experience, Uber had been doing this since before ChatGPT became a thing. It seems like Uber is just experimenting with what number before the ‘%’ sign is going to nudge people to buy more.