Well, security is a pretty big concern, to be fair. The rejection of kdbus was probably political as much as anything else. However, I think that to the degree that there was any kind of consensus, it was not necessarily a rejection of the idea of a kernel-based message bus entirely, but that this particular effort was not up to the mark. This seems to be a fairly relevant bit on LKML:

https://lkml.org/lkml/2015/6/23/22