Because of the poor staffing we have in some large cities. I know it Baltimore he definitely doesn't have it too well. In DC I've had long waits like that too.
Over use of the EMS system when it get real bussy they take a company out of service in each battalion and have them ride a critical alert medic. Worst was during the snow storm they had about 60 ems runs on the CAD at any given time with only 24 front line medics in the city there was alot of waiting.