Earlier quoted context omitted.
What if the driver doesn't want to charge a fee and is happy to just circle the block and drop the item off to a thankful customer, as described in this episode? Maybe things won't be as convenient for some drivers, in which case a fee is appropriate. But imposing a fee without asking the driver or allowing the driver an easy way to notify the customer of the lost item is dishonest; Uber is not doing it on the driver…
The driver chooses to return the item in the first place (and they know the fee), and they can notify riders about lost items via their app. Uber avoids price negotiation, and considering that it takes time and effort to resolve your mistake, it's likely much better to just charge a standard fee instead of planning for every single case.
If my driver is a block away but can't contact me until ops gets back to them and they're miles away, that's an indisputable failure.