Good point, but what if you were previously chaining horse carriage rides and now a car can cover the same distance as 10 of them with a single driver?
You can now deliver 10x the packages and make 10x money.
What healthy business aims to stagnate in the face of a revolutionary technology?
I don't know, maximum package turnover might be bounded and most likely you were previously not constrained by lack of drivers already... Sure you might try and expand but why would that work better than before? Especially assuming all other providers now also have cars.