Uber does almost 1 million rides per hour. About 100 million monthly active users are driven around 26 billion miles each year. Think about all these car locations, requests, passenger details, messages, prices, tips, customer support etc landing into their system every second. Think about price predictions that can be off by just few cents and could make a dent in your earnings or push customers to the competition. Add onto this reliability in at least 3 or 4 nines, latencies across the globe, security, fail-over, multi-platforms, privacy etc issues. Don't forget you need to operate in 700 cities worldwide with all kind of regulations, customizations and geographic/culture adaptation. Uber accomplishes 230,000 trips per employee and earns $500,000 per employee - which is on par with other tech companies. I think you will find that the scaling system without falling on your face every day, every hour is a pretty significant undertaking at this point.