While I think undercutting competition is true, I think there's another aspect - common with food delivery apps.

If Uber (or others) actually charged what it would really cost to perform the service, pay a fair wage, etc - the resulting price would be so high that the average user wouldn't accept it.

The only way they've been able to get any interest at all is by finding every possible way of keeping the price way lower than it should be. Mostly be underpaying drivers.