Like many/most public companies, Apple doesn't work for cash cows (it's the other way around) but their real customers - shareholders.
Shareholders are owners and shareholders want money. The way to get money is from customers. You don’t make money from shareholders unless you’re running a Ponzi scheme.
Customer is a recipient of goods provided by seller or vendor in exchange for money or other valuables. User of free service is not a customer by that definition. Unless you would openly treat privacy as currency.
Investor who gave a company money is - in my view - a paying customer. They give a business some cash, expecting more in return. It is not paying for service but it is still paying and expecting something in return. A publicly traded company is a product itself and investor is buying that product.