Why Digital SLR cameras do not have movie-mode?

The main reason is because the SLR which stands for Single Lens Reflex has a mirror that blocks the sensor and therefore does not allow continuous exposure to it. DSLR was designed purely for image quality. The majority of DSLR have a combination of electronic and mechanical shutters. It is this mechanical device that limits the exposure time (Unlike CCD's in compact digital cameras whose sensors are derived from video CCD's).
There are however, two DSLR's that do have live video, however it is expensive and the sensor has a limit of 30 seconds of live video before the sensor has to cool down. The camera operations are limited to viewing the live feed but nothing else can be done. No picture can be taken whilst this is occurring.

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