He also found that drivers often handed out business cards to encourage repeat customers to pay them directly (avoid taxes+Uber, etc). Further, customers abused drivers various times (e.g. it's used as a cheap moving service incl expecting you to carry boxes), etc.
Entire article (use Google Translate): https://www.volkskrant.nl/kijkverder/2017/uber/
That said, Dutch people tend to be (let me say it nicely) 'very considerate on their spending patterns'.
The biggest object I've moved with Uber was a 40" TV which I carried and placed in/removed from the trunk.
What I know from talking to people is that the Uber drivers used to make above average wage after taxes and expenses. Now Uber takes a bigger cut and there is competition, so it's below average. Also you get a car with all expenses paid.
I think the problem is that in Europe the state covers healthcare and other benefit so Uber drivers are doing alright here.