DSLRs just don't have the types of lenses and a ton of electronics and features that are in broadcast cameras. Broadcast cameras have things like 3-CCD sensors, built-in variable ND filters, reference/sync inputs, multiple video outputs (clean, pix) over SDI or SMPTE 2110 or connectivity to a CCU (camera control unit). They'll often support intercoms and return video for the camera operator or for teleprompting. Source: am broadcast engineer.