[aaronwall]

Big brands have the ad budget to advertise. That drives awareness. If they have offline stores, those can be thought of as both destinations AND interactive billboards which drive further brand awareness and demand for branded searches.

Many of the top search queries are navigational searches for brands.

And so if tons of people are searching for your brand then if there is a potentially related query that contains the brand term & some other stuff then they'll likely return at least a result or two from the core brand just in case it was what you were looking for.