Uber/UberEats driver here with a few thousand rides. I'm retired from a technical professional career in California. I don't want to give out more info because I don't want to get deactivated. It's a fun job and I love talking to people and being out having a look around.

Uber shot itself in the foot in two ways in regard to that big percentage going towards driver incentives

A. Uber trained people not to tip so only 10% of them do.

B. Uber drivers do both ride share and Eats in the same app. They can turn off one or the other or do both. There often aren't enough Eats drivers as a result (more to follow)

A cont...
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People always used to tip taxi drivers, but Uber said "hey you don't need to tip on Uber" and implied or outright said tips are included. Often rides are not profitable without a tip, so drivers refuse them or cancel them. For example, driving 10 miles to give someone a 2 mile ride. So Uber has to gamify and pay incentives for consecutive rides or whatever (I ignore the games, because I do Lyft as well. I make more doing both, rather than playing the games)

Here's what Uber has said over the years about tipping:

March 30, 2014
https://web.archive.org/web/20140330002844/https://www.uber....
From the rider landing page:
CASHLESS & CONVENIENT You don't need cash when you ride with Uber. Once you arrive at your destination, your fare is automatically charged to your credit card on file – no need to tip. We’ll also e-mail you a receipt.

From the help:
Tipping Drivers
Being Uber means there is no need to tip.

Mar 31, 2017
https://web.archive.org/web/20170331040415/http://www.uber.c...
Do I need to tip? The Uber app cannot include a tip when billing you for a trip fare... In most cities, Uber is a cashless experience. Tipping is voluntary. Tips are not included in the fare, nor are they expected or required. As a rider, you are not obligated to offer your driver a gratuity in cash. If you decide you would like to tip, your driver is welcome to accept.

Today
Can my driver ask for a tip? Drivers may request tips at their discretion. Drivers care about rider ratings and do their best to create an ideal trip experience. While Uber does not require riders to offer drivers a tip, you are welcome to do so in cash, through the app, on riders.uber.com, or from your emailed trip receipt. Please note that the trip fare charged to your payment account does not include a gratuity.

B cont...
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By doing UberEats in the same app and subjecting Eats drivers to the more stringent standards required of passenger carrying drivers (nice car, spotless background check) they eliminate a lot of Eats drivers, who may have an older car or minor traffic citation. Not only that, but why do Eats when Uber rideshare is busy? (and Lyft is busy, since most drivers do both) With Eats, you have to get out of the car, fight your way into a busy restaurant (Fri,Sat night) deal with surly restaurant personnel. Then, drive to some apartment complex, get out and look for the apartment in the maze, or drive to a house on a dark street and look for the right house number, which is barely visible in the dark or doesn't exist. Then try to find the front door (some will come out and meet you, but not many) Then on top of that not get a tip. You don't have to tip Uber, remember. Eats tip rate is a little higher.

Conclusion: Because Uber had told people that they didn't have to tip and that got into the zeitgeist, only 10% of them tip. Uber has to offer bigger driver incentives as a result. Would less people use Uber if they felt they had to tip? Yes, that's why Uber said people don't have to tip. At the time, there were less drivers and I hear anecdotally from other drivers that the money was better than now, even without the tips. Waiters, Bar tenders, many others make good tip money, but that horse has left the barn for Uber and now they can't retrain people to tip.

UberEats is a second class job for Uber/Lyft drivers. It would be better as it's own app with less stringent rules. There would be more drivers and they would get there faster.

If I am wrong about any of this, I welcome someone pointing that out. Thanks for reading.