I tend to assume the reason why we see so much advertising is because they _don't_ make that calculation.
That would be true for the old media. OTOH, online advertising is extremely data-oriented, especially in the US. Most business decisions are based on data. Businesses may be using wrong models or assumptions about the correlation or causation between advertising and revenue, but there is a very strong effort to analyze data for revenue growth.
I'm kind of assuming that every company doing advertising is continually making that calculation, and deciding that it does come out in their favour. Otherwise we wouldn't see nearly so much advertising.