If they enforced the laws in DC, the criminal element would have shifted to the outlying areas. It's like spraying for roaches in one apartment - it only shifts them to the other apartments.
By design, Democrat cities are run as an open air prisons / insane asylums / urban reservations, to keep the outer areas functioning and contributing to the financial system. They just don't tell you that in the marketing brochures and government reports.
It certainly works that way, but I doubt its the product of "intelligent design."