1. Modern digital ads can be very well measured. At least the ones focused on direct conversion and not branding. Advertisers can measure the impact of their spending independently and the results can be seen fairly quickly. (Again, not brand advertising).

2. Advertisement match-making isn't perfect (which is why I wrote "in an ideal world"). There is some time and signal buffer till we get enough signal to show the right ad to the user (if ever). The intentions of the ad platform also have to be taken into consideration (Often not the case for Big Tech but even here).

3. Advertisements do have negative consequences. We can also target drugs, cults, gambling etc more effectively as well. Often the law has to play catch-up with the more controversial categories. Advertisers can also dupe/defraud buyers with false/misleading advertisements.