I think that has to do with the whole concept of fate. Campion was told by Death itself that he needed to carry out the mission. I would assume that would mean that the Black Rabbit wouldn't actually take him until his task was complete. So, it probably tampered with a few things to avoid having Campion die prematurely. For example, what are the chances that Skree would save him the same day Pipkin befriended Skree (much less a rabbit befriending a hawk in the first place)? Campion said it himself when he led the Darkhaven army: the Black Rabbit told him he wouldn't fight Woundwort alone, so he trusted that he should take them to Watership Down despite the risks.
Now, yes, he did some undeniably stupid things (Go ahead and exchange dangerous information in the middle of Darkhaven with Blackberry, Campion. See what happens when you're inevitably overheard). But that probably was just a way to build up suspense. Either way, what the Black Rabbit said was true despite the bad decisions, so that would have to be my best guess.
Forgive me if I said anything blatantly incorrect. It's been a while and I don't exactly recall everything the Black Rabbit actually told him.

became such an interesting character in season 3 in my opinion. His motives are really hard to understand, though...