While that's true, how many of us are not going to have a knife on us when we head into the woods?

Given we have a knife anyway, it usually takes no more effort to carry one's knife in an easily accessible position (not necessarily tip up) than it does to lash it on the back of a pack or tuck it away in some compartment. This would seem to be the type of low cost / low effort risk mitigation strategy appropriate for a low probability / high consequence risk like a wildlife attack.

Between this and the type of possible risks ireckon mentioned earlier in the thread, it seems like a good idea to have quick access to a knife at all times.