A marketing campaign with that rate of success would be an abysmal failure.
In short, enough people respond to a Nigerian scam to make it one of the country's biggest industries. And that requires constant, active participation in the face of a blatant scam that gets less plausible at every step. Passively allowing your perception to be shaped by how an idea is presented is many orders of magnitude easier.
And falling for a Nigerian scam requires a much higher level of gullibility and a higher level of buy-in from the victim than merely letting somebody else set your expectations with careful phrasing.
My point isn't that everyone would fall for it, but if there are enough people who fall for more blatant scams that you can build a hugely profitable business off them, there's certainly a considerable number who would fall for this.