That is pretty shitty. It use to be that drivers had to return stuff on their own dime, I think the fee is supposed to pay them for that time.
And if you read the other comments, you would see that direct communications can be abused so this current process is likely the best compromise to help both riders and drivers.
And as stated before, many drivers return items immediately for free while many others probably don't find items until days after the original rider reports it, so there are vastly different scenarios under which you need a process to work.
Is the tiny detail of whether the driver can set the exact fee really that important?