[onlyrealcuzzo]

Also, blind humans (and bats) can walk (and fly) around the city pretty easily with just sound. Why would you tie your hands behind your back and try to make a robot that can navigate the city using only sound?

To cut corners and costs.

Point #2 is deeply flawed.

[dgut]

Not really a good example. Blind humans don't navigate cities easily, even when cities take them into account. As an example, crossing a street despite tactile surfaces on each side can be a hassle because it's difficult to tell if you're walking straight or diagonal towards the other end, potentially walking into a car. Sound only takes you so far.

Source: I have blind friends.