There are a few answers. One, they can. They have the luxury of having massive budgets to work with. Two, big established brands often times are corporations that answer to shareholders, and the role of a corporation is acquisition, and distribution of wealth back to the shareholders. This drives the need to keep spending big dollars to win over the competition. Three, that’s marketing. The role of marketing is to continually raise awareness to increase business. Four, marketing efforts such as volume based digital advertising (PPC and SEO) in the big picture is easy and automated, but inefficient. The ROI compared to other forms of marketing is less, but it’s easy for big players to throw a lot of money at it.
The caveat to all of this is often they could more with a smaller budget. There is a disconnect between marketing and sales. Because the marketing wing is not in touch with the sales department, they focus on brand, position, and how the product is perceived instead of how they can help drive sales. You’ll see in big corporations this type of inefficient spending because no one is talking to each other. If the head of marketing was in control of, or directly influenced, the sales department, with a bigger responsibility for both the spend side and the revenue side, it would be a different ball game. But that’s rare at the corporate level.