To mainly answer your question, because it is (supposed to be) more convenient for foreigners. To a foreigner, Chinese characters do not make any sense. But that's probably not what you are aiming at. These "people"  could indeed write Chinese street names in PinYin. That would be more logical. It disturbs me how i.e. companies provide you with their English address and not provide their Chinese written adress along with it. Occasionally I have difficulties with finding a place location on baidu, google, bing or the like. So I hope, one day, the Chinese will include their Chinese address as well. For the taxi-driver's sake at the least.

Aside from the ring roads I can't think of any. 

Because you're not allowed to use the five letter "L" word around here.  (actually that can be the answer to any question when something just doesn't make sense and someone asks "why")

it isnt strange about this thing, our people (chinese)like foreigners think our city is a big international metropolis, so we translate the street names to  make you feel more conveniences. but as your question ,the result not  good

I find it much less convenient, mainly because they are very inconsistent about translating words like 路, 街, etc, and the taxi driver doesn't understand English.

Complicating matters, if I ask for the Chinese name, the person I'm asking might get offended as if I'm suggesting their English isn't good enough. Actually, all I want is something to tell the taxi driver.