a/b tests only work for outcome based advertising. A lot (if not more) of the old world advertising isn't outcome based. It's more about make consumers hear your brand over and over and be associated with things that you think of them automatically.
The descriptions I've read about a/b testing make it sound a lot like null hypothesis significance testing, which has a well earned reputation in the social sciences. And you have to buy the things that you're testing, either from a vendor, or by employing people who assemble the stuff.
Advertising signals are normally too weak to be detected by standard A/B tests.
Additionally, most traditional advertisers do not run A/B tests. Their agencies especially do not run such tests.
Source: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=lewi...
