It's not really that it's an exception to Goodharts Law, it's that Goodhart's Law only applies to measured proxies. If the goal of a company is first and foremost to make money, then sales is the only organization within the company that can be measured exactly according to the primary goal of the company rather than a proxy.
Goodhart's Law still applies to the extent that companies have other goals and sales's incentives totally screw those goals up. But they are very effective incentives at increasing money earned.
Goodhart's Law still applies to the extent that companies have other goals and sales's incentives totally screw those goals up. But they are very effective incentives at increasing money earned.