Why do brands open up stores in a mall where they would have competitors?

Why wouldn't they just open their store outside of a mall where would be less competition? Every mall has several brand name stores that directly compete with each other. Wouldn't it be harder to compete in a mall vs. opening your location in a dedicated space?

Short answer: You want your store to be where the customers are.

If you have competition, who are in a mall, there's little point you being in another part of the city, where there may be less competition, but, no customers.

Even if you find a spot, where there are customers and no competition - what do you think will happen when the competition sees you gaining a dominant position?

I'm not sure about the authenticity of the anecdote, but it illustrates the point well: I was once told that US pharmacy brand Walgreens spends an awful lot of money on research for where they should place their stores. Their competitor, CVS, on the other hand, spends very little money on research - they simply put their stores within sight of Walgreens stores.