Precisely because eBay, knowing they were buying into a frugal-first operation like Craigslist, specifically structured the deal such that it was owed this duty. That Craig and Jim took the money under those terms is on them, as is their failure to honor the terms of the contractual duty they owed eBay for its minority stake, specifically including all the ways they tried to weasel out of the deal — for which eBay did have a legitimate cause.

From what I've read, if eBay had not bought that stake under those specific terms, there wouldn't have been a case here. (Or at least not this case.)

Again, IANAL, but I think that makes it more of a contractual duty case. A dog wearing a bill and wings, with a collar that quacks, is apparently a duck — if your lawyer is good enough…