This isn't the case. Uber repeatedly, and likely fraudulently, claimed that they were profitable ex-growth markets (iirc, they made this claim shortly before their IPO, I remember it being leaked to compliant journalists). They have never attempted to obtain a global monopoly either (they bought stakes in companies outside the US, which clearly wouldn't have given Uber itself scale economies). The only place that you saw people make the claim about driverless cars was on Reddit, management never made that claim...because it makes no sense.

The underlying business can, obviously, be profitable. There is a guy near me who runs a taxi app, town has a population of ~5k people (no city with an Uber taxi service for miles around), and he is profitable. The problem is that most tech companies are run by morons who have a big stack of other people's money to burn (it really is that simple, all of these companies thought this day would never come...it has come, it is today).