the difference is in the details. what you say is incredibly hard. they set up a global service in thousands of legal jurisdictions that let's you use one app. in rome you can only legally get a black mercedes qualified as a limo. in dubai you can order a lexus taxi or an uber helicopter. in chicago anyone with a car can be an uber. in moscow they have to go through yandex taxi. to me, in any city with all its different rules, I pop open an app, order what i want, and it just gets charged to my amex. they handle insurance rules, they handle refunds and disputes, they provide mapping software drivers use - worldwide, so you can look at your route and not get ripped off by a cabbie. they provide car leasing services to drivers like a dealership.

this is an insanely complex feat to accomplish. it's also expensive.

what does a taxi service do? it's a guy sitting at dispatch assigning calls to cabs.

the stock exchange is complex too. not nearly as complex, with much more well-defined and common rules. but even they don't just charge you. they also charge listing fees, regulatory fees, governance, access to data fees, and sell services and software for trading. you are also comparing a trade transaction to a cab ride. sorry, a cab ride is a much bigger and more involved thing than a button you click on a website.