Reach is just one aspect of brand awareness. Potential customers can't be aware of your brand if they aren't exposed to them in the first place. Brands can extend their reach in a number of ways, from advertising to a wider audience to making their product or service more available to expanding their target markets.
In a nutshell, if you want your brand to be remembered, you'll want to work on brand awareness. If you want your brand to reach the most amount of people, you'll want to work on reach.