It is becoming increasingly difficult to demonstrate the ROI of online advertising clearly. Uber just run an experiment by turning off 2/3 of their ad spending ( $100M out of $150M). Uber discovered they’d been defrauded as there was no change in buying behaviour.
Sure, TODAY, it doesn’t have the impact they’d like it to have, but the investments PRIOR were key to ensuring their success.
In the end, it is still hard to quantify the real ROI, how much is wasted, how much has any impact.