not saying all dnb djs tend towards the boring and excitement-free, mate. just that the scene doesn't generally ask much of its djs, or perhaps a better way to put would be that the scene is flooded with even more bland djs than normal for electronic dance music. for as long as i can remember, most dj sets have relied on the tracks having dramatic breakdowns, and an MC going on about something or other. so why bother even making a CD in advance? you can be a perfectly mediocre dnb dj with less hassle :)
(obviously it's better to approach music with some thought and effort, as you say)