Because, as a longish-time resident of the area between West Roxbury and Jamaica Plain, I can assure you it is not called Metropolitan Hill or Centre-South. And I'm pretty sure we don't border Upper Washington.
Ed. note: Yes, there is a Metropolitan Hill. It's one single hill in Roslindale, right next to Grew Hill. But unless you're talking to somebody who lives on Poplar Street, you'd never say that to somebody who asks where you live. Centre-South? Try "Roslindale Village" or "the Arboretum," if you must. Upper Washington? OK, sounds classier than boring old "Washington Street."
