You have to keep in mind how cheap advertising is. An ad campaign that affects one in a hundred thousand can be successful.
In some areas, you'll find a ton of billboards for personal injury lawyers. Right off the bat, maybe only one in several thousand people is a potential client, and it's totally irrelevant to the remainder. Of the relevant population, most of them have the common sense not to hire a lawyer purely based on an advertisement. But those billboards are still worth it. They know because they ask people how they learned about them, making it simple to calculate their value.
In some areas, you'll find a ton of billboards for personal injury lawyers. Right off the bat, maybe only one in several thousand people is a potential client, and it's totally irrelevant to the remainder. Of the relevant population, most of them have the common sense not to hire a lawyer purely based on an advertisement. But those billboards are still worth it. They know because they ask people how they learned about them, making it simple to calculate their value.