It turns out there are some problems.
One is the pay-to-play problem https://en.wikipedia.org/wiki/Pay_to_play that opens up all sorts of ethical issues. Consequently, many companies prohibit their execs from entering into arrangements like this.
Even beyond that, bypassing the traditional gatekeeping methods through a cash payment is exactly that -- a bypass method.
And assuming those traditional gatekeeping methods are in place to protect the executive's time and the company's reputation, it's just not something that a lot of truly powerful and smart execs will be on board with.
That doesn't mean there aren't a lot of expert-as-a-service consulting companies https://en.wikipedia.org/wiki/Expert_as_a_service but generally their experts only perform consulting, rather than letting you pay to pitch them your product.