There's massive efficiency gains. The countless one man businesses have no overhead side from owning a car they already have. They don't need to do anything else besides install and run an app. No need for marketing, managing payment systems, customer acquisition...etc Millions of drivers globally have the business side of things taken care of by a single company. Fragmentation across tens of thousands of taxi companies is inefficient.

In the US many neighborhoods and entire cities didn't have access to reliable taxis or any taxi at all. There's significantly more coverage with Uber and ride sharing in general. The same is probably true of other countries.