Maybe because Exxon charges for their product, and Google supplies it free?
Then where do those profits come from? A PayPal tip jar?
No, Google charges- and a huge percentage, in fact- for ads, they license the Android OS, they own and get royalties for thousands of patents, etc. etc.
On the other hand, the product that the oil companies produce, under heavy scrutiny, and for which they make a lower pforit margin than Wal-Mart, literally fuels every single thing a person buys or consumes in a day. From the jet fuel for over 100,000 flights a day, to all the product and produce moved on container ships, to trucked via semi, to hauled by train. The coal you statistically likely consumed to get the electricity you're reading this with, was almost certainly shipped via diesel-electric train. The computer came from Asia on a cargo ship, and the can of soda sitting nearby (or bottle of water, or package of Twinkies, or whatever) was trucked to you from a distribution warehouse.
Yes, you have bought Exxon fuel. Many times. Even if you buy only from a competitor, they very commonly trade and transfer both crude and finished products, depending on who has capacity or storage to spare.