The sad reality is anything that is funded through advertising is going to hit plateaus in the coming years. We've just been oversaturated with it, its become a burning pot for companies to throw money into with no ability to properly attribute it. I can't remember _ever_ buying something as a direct result of advertising.
That isn't the point of (most) advertising. The point is to get the brand or product into your mind and make it familiar. That way, when you are in the market for Product X, you'll think of Brand Y due to their podcast ads.
