Like I know McDonald’s exists and there is a 70% chance there is one at the next exit, why do I need 4 billboards telling my there is a McDonald’s coming up in 5 exits?

Same reason there are coca-cola ads even though everyone knows about it.

These companies know the value of dominance in the advertising market. The more we see their ads, the more successful we think they are and the more acceptable it becomes to use their services.