From the perspective of an Uber driver, my experience is that Uber doesn't "eat" anything. The driver will see their earnings for the day drop. And I mean literally drop as opposed to seeing a physical adjustment posted. Even going through the day's trips one-by-one and "expanding" them to see the earnings calc in detail, doesn't give a clue as to why (or even on which trip) the earnings were adjusted downwards.

It doesn't happen often, but the driver not having any knowledge or say in the matter can be frustrating.

There was one time when I knew which trip adjusted downwards. In challenging it, Uber basically told me I was lying.
IT was getting late and a drop-off had me relatively close to home, so I decided to quit for the day. Plus an NFL home game was about to let out and Uber had already started the "head towards the stadium, you will make $$$" pings. I avoid major events like the plague (talk about problems in hooking up the driver with the customer !!!! ).
But as I entered my neighborhood (way out in the suburbs), I noticed it was running at 1.8 surge (supply vs demand ... the rider's fare, thus the driver's payout .... is at 1.8 times the normal rate).
I don't really believe in surge pricing and most certainly don't drive out to surging areas specifically trying for the higher rate. But in my own neighborhood and I'm already there, why not. So back on-line I go and I get a ping right away.
The pickup was 15 minutes away, but was marked as "over 45 minute ride" (driver's don't know where a ride is going until after the pick-up). From my area, "over 45" usually means an airport run and that's what this ride was.
The customer complained about the fare being higher than normal. I explained that it was probably the NFL game and (shooting myself in the foot while being honest) said Uber entices drivers to head towards the stadium, thus leaving other ares under-covered.
So I drop him off and note my earnings for the one trip was $50.xx. From my area to the airport I typically earn $28-30.
By the time I get home and log the day into my spreadsheet, my total earnings had dropped. Suspecting that last ride, I checked and it was now showing $28.50

I can see the customer's view. The surge price was NOT created by customer demand. It was a short supply of drivers caused by Uber's manipulation of trying to get drivers out to the stadium.
But from my view, I was ready to stop for the night. It was UBER showing surge pricing that lead me to keep working and pick up this passenger (he also complained about having a 15 minute pick-up time .. without me it would've been longer).
I assume the passenger called Uber while waiting for his flight and complained about the fare. If UBER decides to adjust to a 'normal' fare in the name of 'customer service' then THEY should eat the difference, not the driver.

Multiple emails back-n-forth with me challenging the adjustment had Uber claiming that the area was never in surge, this specific fare was never calculated as surge and it was never adjusted and finally it's obvious that I don't understand how to use the Uber Driver App.
Going forward from my complaint, I can no longer can my earnings for a specific trip withing a few minutes of drop-off. I only get "we're still calculating the fare" for about an hour or 2. Coincidence ??