The cheapo mass produced "can" motors you are using are not (as Bill points out) very efficient. While you can find high quality brushed motors are actually more efficient than brushless.
I agree that the biggest downside is the brushes wear out (sometimes quickly) and they tend to be heavy, have gearboxes (so more moving parts and weight) and no longer have a cost advantage.
So you can save weight, have fewer moving parts (with outrunners) and longevity. Now they are as cheap as brushed. They are MUCH more powerful for their weight compared to brushed. Another great feature.
So why not?